SB    51    SIB 


EDUCATION  DEFT, 


JUNIOR    SCIENCE 


BY 

JOHN   C.  HESSLER,   Pn.D, 

ASSISTANT    DIRECTOR,    MELLON 
INSTITUTE,    PITTSBURGH 


BOOK   ONE 


BENJ.    H.    SANBORN   &   CO. 

CHICAGO  NEW  YORK  BOSTON 

1921 


" 


COPYRIGHT,   1920, 

BY  JOHN  C.  HESSLER. 

gpUCATlON  DSP* 


PREFACE 

IT  is  almost  a  truism  to  say  that  science  is  the  foundation 
of  modern  civilization,  yet,  curiously  enough,  educators  have 
largely  postponed  the  study  of  science  to  the  later  years  of  the 
school  course.  This  is  especially  true  of  the  fundamental 
sciences :  Physics  and  Chemistry.  As  a  result,  few  of  the 
young  people  who  go  to  school  ever  study  the  physical  sciences 
at  all  and  these  few  only  at  the  end  of  their  student  careers. 

To  say  that  most  students  have  not  studied  science  is  not, 
of  course,  to  say  that  they  have  not  had  any  practical  experi- 
ence with  the  facts  of  science.  Merely  to  state  such  a  proposi- 
tion is  to  disprove  it.  From  their  earliest  years  children  are 
obliged  to  adapt  themselves  to  conditions  caused  by  gravita- 
tion, inertia,  heat,  air  pressure,  convection,  and  the  like ;  they 
soon  learn  to  use  all  sorts  of  mechanical  and  electrical  devices : 
but  they  experience  these  phenomena  and  use  these  devices 
empirically,  without  the  clarifying  influence  of  scientific  ex- 
planation and  without  the  inspiration  and  enlargement  of  vision 
that  would  come  from  the  scientific  way  of  looking  at  them. 

With  so  little  opportunity  for  science  in  school,  is  it  any 
wonder  that  the  child  comes  to  feel  that  he  must  pursue  the 
quest  of  the  great  natural  "whys"  of  his  life  outside  of  the 
school,  or  that  he  must  not  have  so  many  troublesome  ques- 
tions surging  through  his  mind?  A  host  of  school  children, 
it  is  to  be  feared,  find  the  latter  way  the  easier  and  drop  out 
of  the  ranks  of  those  who  wonder.  Then,  all  too  late,  educa- 
tors realize  that  they  cannot  get  such  children  interested  in 


iv  PREFACE 

science.  It  is  well  known  that  normal  children,  if  given  the 
opportunity  to  seek  scientific  answers  to  their  problems  at  an 
early  age,  do  not  need  to  be  "interested"  in  science ;  they  have 
the  interest  as  a  native  endowment.  A  child's  natural  eager- 
ness to  understand  the  phenomena  he  meets  in  life  is  so  great 
that  it  is  scarcely  true  that  he  needs  to  BE  TAUGHT  science; 
it  is  more  nearly  true  that  he  needs  an  opportunity  to  LEARN 
science  and  to  put  it  to  use.  Science  teaching,  moreover, 
does  not  consist  in  getting  a  pupil  to  answer  the  teacher's 
questions,  nor  yet  in  getting  the  teacher  to  answer  the  pupil's 
questions,  but  in  training  pupils  to  ask  and  to  answer  their 
own  questions.  Upon  the  ability  to  see  quickly  what  is  taking 
place,  to  understand  the  reason  for  it,  and  to  know  how  to  deal 
with  it,  not  only  the  progress  of  the  individual,  but  also  the 
life  of  the  nation  depends.  Science,  which  demands  observa- 
tion and  reasoning,  therefore  yields  to  no  branch  of  knowledge 
the  position  of  first  importance  in  our  modern  life ;  it  should 
have  a  similar  place  in  our  educational  system.  It  is  not  an 
elective  appendix  to  the  course  of  study,  but  the  sine  qua  non 
of  an  efficient  curriculum.  The  proper  pursuit  of  science  will 
give  the  child  the  opportunity  not  only  to  know  the  world  of 
which  he  is  a  part,  but  to  know  also  his  relation  and  responsi- 
bility to  that  world.  Right  knowledge  is  the  only  sure  founda- 
tion for  right  action. 

It  is  to  meet  the  science  needs  of  the  students  and  teachers 
of  the  Junior  High  School  and  of  the  corresponding  grades 
elsewhere  that  Junior  Science  is  written.  Nature  Study  may 
be  pursued  in  the  earlier  grades,  but  grades  seven  to  nine,  in- 
clusive, are  ideal  for  the  beginning  of  a  definite  study  of  science. 
In  the  writing  of  the  text  the  age  of  the  pupils  of  these  grades 
and  their  degree  of  attainment  have  been  kept  constantly  in 
mind.  This  statement  applies  both  to  the  quantity  of  material 
selected  and  to  its  kind.  The  style  of  the  book  is  simple. 


PREFACE  V 

The  section  titles  are  nearly  all  queries ;  many  questions  are 
also  asked  throughout  the  text,  as  well  as  in  the  exercises  at 
the  end  of  the  chapters,  in  order  that  the  student  may  be  kept 
open:minded  and  alert.  The  author  is  confident  that,  by  using 
the  desire  of  boys  and  girls  to  know  the  reasons  for  many  things 
they  are  now  doing,  the  teacher  can  arouse  them  to  know  the 
"why"  and  the  "how"  of  the  duties  that  await  them  here- 
after. 

The  text  consists  of  two  divisions :  Books  I  and  II.  Book  I 
contains  four  Parts,  distributed  into  twenty-two  chapters :  - 

Part     I :  Introduction. 

Part    II :  The  Atmosphere  and  Its  Relation  to  Man. 

Part  III :  Matter  and  Energy  in  Earth  and  Sky. 

Part  IV :  Science  in  the  Household. 

Book  II  consists  of  three  Parts :  - 

Part     V :  How  We  Use  Nature's  Forces. 

Part    VI :  Living  Things  and  Their  Relation  to  Us. 

Part  VII :  Our  Bodies  and  How  to  Care  for  Them. 

In  the  preparation  of  this  textbook  the  writer  has  been  greatly 
assisted  by  his  wife,  Maud  C.  Hessler.  He  is  also  much  in- 
debted to  his  daughter,  Miss  Margaret  C.  Hessler,  of  the  Uni- 
versity of  Texas,  and  to  Mrs.  Margaret  Honeywell  Miller, 
recently  of  the  Harlem  Hospital,  New  York  City,  for  the  prep- 
aration of  necessary  material.  Most  of  the  drawings  for  the 
illustrations  were  made  by  Professor  Robert  W.  Lahr,  of  the 
James  Millikin  University,  and  by  Mrs.  Lahr.  Several  were 
made  by  Mr.  W.  F.  Henderson,  of  the  James  Millikin  University. 
Photographs  for  the  half  tones  were  obtained  from  the  Mcln- 
tosh  Stereopticon  Company,  Chicago,  the  International  Stere- 
ograph Company,  Decatur,  111.,  the  Old  Colony  Insurance 
Company,  the  Judd  Laundry  Machine  Company,  Professor 


VI  PREFACE 

Frederick  Starr,  Dr.  Thomas  B.  Magath,  and  from  Mr.  A.  M. 
Lythgoe,  of  the  Metropolitan  Museum  of  Art,  New  York  City. 
Several  illustrations  are  reproduced  from  Hopkins'  Physical 
Geography  by  the  courtesy  of  Professor  Hopkins. 

To  all  those  who  have  assisted  him,  as  well  as  to  the  many 
writers  on  science  whose  work  has  made  this  book  possible, 
the  writer  wishes  to  express  his  thanks  and  obligation. 

J.  C.  H. 

DECATUR,  ILLINOIS 
December,  1919 


CONTENTS 

PART  I 
INTRODUCTION 

CHAPTER  I  PAQB 

Beginnings  of  Science .3 

Some  questions  to  think  about.  —  Old  and  new  answers.  — 
What  is  science  ?  —  What  is  an  experiment  ?  —  Why  study 
science  ?  —  What  we  have  learned.  —  Exercises. 

PART   II 
THE   ATMOSPHERE  AND   ITS  RELATION   TO  MAN 

CHAPTER  II 
Air 13 

What  is  air  like  ?  —  Does  air  take  up  room  ?  —  Does  air 
have  weight?  —  Is  air  matter?  —  How  do  heating  and 
cooling  affect  air  ?  —  Can  air  be  compressed  ?  —  For  what 
can  compressed  air  be  used  ?  —  Exercises. 

CHAPTER  III 
Pressure  of  the  Atmosphere         .         .         .  •      .         .  .21 

Does  the  atmosphere  have  pressure  ?  —  Can  the  atmos- 
phere's pressure  be  measured?  —  The  barometer.  —  Is  the 
atmosphere's  pressure  always  the  same?  —  Exercises. 

CHAPTER  IV 
Fire 26 

What  does  fire  mean  to  us  ?  —  How  are  fires  started  ?  — 
How   does  a  fire   burn  ?  —  Experiments   with   burning.  — 

vii 


Vlll  CONTENTS 

PAGE 

How  much  of  the  air  supports  burning?  —  Is  air  a  mixture? 
—  How  can  we  explain  burning  ?  —  What  is  a  flame  ?  — 
Exercises. 

CHAPTER  V 

Oxygen,  the  Fire  Gas  . 36 

How  can  we  prepare  oxygen  ?  —  What  is  oxygen  like  ?  — 
What  is  oxidation  ?  —  Why  does  paint  harden  ?  —  What 
are  rusting  and  decay  ?  —  Exercises. 

CHAPTER  VI 

Carbon  and  Carbon  Dioxide 42 

Why  do  some  substances  char  ?  —  What  is  formed  when 
carbon  burns  ?  —  How  can  we  make  carbon  dioxide  ?  — 
What  is  carbon  dioxide  like  ?  —  Why  does  soda  water 
foam,  or  effervesce?  —  How  does  carbon  dioxide  put  out 
fires  ?  —  How  does  carbon  dioxide  get  into  the  air  ?  —  How 
is  carbon  dioxide  removed  from  the  air  ?  —  How  do  plants 
help  animals  ?  —  Exercises. 

CHAPTER  VII 

The  Air  We  Breathe 52 

Why  do  we  breathe  ?  —  Why  do  we  need  ventilation  ?  — 
Fresh  air  and  tuberculosis.  —  How  do  we  ventilate  our 
houses  ?  —  How  can  we  ventilate  our  bedrooms  ?  —  How 
to  ventilate  the  schoolroom.  —  Do  we  need  moisture  in 
the  air  ?  —  How  do  we  breathe  ?  —  Proper  and  improper 
breathing.  —  Exercises. 

CHAPTER  VIII 

Heating  the  Air  of  the  House 61 

How  do  we  heat  the  house?  —  Fireplaces.  —  Stoves.— 
How  does  a  fire  warm  us?  —  Hot-air  furnaces.  —  Heating 
by  hot  water.  —  What  is  steam  heating?  —  How  can  we 
know  the  temperature  of  the  house  ?  —  How  is  a  ther- 
mometer made?  —  The  two  thermometer  scales.  —  Ex- 
ercises. 


CONTENTS  IX 

CHAPTER  IX 

PAGE 

More  About  Heat 71 

Are  heat  and  temperature  the  same  ?  —  Can  heat  be 
measured  ?  —  Is  heat  needed  to  melt  ice  ?  —  How  does  the 
body  keep  its  heat  ?  —  Why  does  perspiration  cool  the  body  ? 

—  Exercises. 

CHAPTER  X 

Weather .77 

What  is  the  weather  ?  —  Of  what  is  the  atmosphere  com- 
posed ?  —  What  causes  dew  and  frost  ?  —  How  are  clouds 
formed  ?  —  Why  do  we  have  rain,  snow,  and  hail  ?  —  What 
is  rainfall  ?  —  What  are  the  winds  ?  —  What  causes  our 
great  storms  ?  —  What  is  the  weather  service  ?  —  Exercises. 

PART  III 
MATTER  AND   ENERGY   INEARTH  AND  SKY 

CHAPTER  XI 
The  Heavenly  Bodies 95 

What  is  the  earth  like?  — What  is  the  sky?  — Why  do 
the  heavenly  bodies  rise  and  set  ?  —  What  is  the  path  of  a 
star  across  the  sky  ?  —  What  are  some  star  groups  ?  — 
How  far  away  are  the  stars?  —  Why  are  some  heavenly 
bodies  wanderers?  —  What  is  the  sun  like?  —  What  is  the 
solar  system  ?  —  Our  neighbor,  the  moon.  —  What  are 
comets  and  meteors  ?  —  Exercises. 

CHAPTER  XII 
Force  and  Energy .     112 

What  holds  the  solar  system  together  ?  —  Why  does  a 
body  have  weight  ?  —  In  what  direction  does  the  earth  pull  ? 

—  What  is  the  density  of  water  ?  —  Why  does  a  body  float  ? 

—  Can  you  stand  an  egg  on  end  ?  —  Can  a  body  move  itself  ? 
-  Why  does  a  pendulum  swing  ?  —  What  is  a  force  ?  — 

When  has  a  body  energy  ?  —  Why  do  objects  fly  from  the 
center  ?  —  Why    do    planets   revolve   around    the    sun  ?  — 


X  CONTENTS 

PAGE 

Is  there  any  force  in  a  water  surface?  —  Why  does  a  blotter 
absorb  ink  ?  —  Exercises. 

CHAPTER  XIII 

Substances  .  127 

What  is  a  substance  ?  —  Can  substances  be  changed  ?  — 
Can  water  be  changed  ?  —  What  is  an  element  ?  —  How  can 
we  prepare  hydrogen  ?  —  What  is  hydrogen  like  ?  —  What 
is  formed  when  hydrogen  burns  ?  —  Do  our  fuels  contain 
hydrogen  ?  —  Is  salt  an  element  ?  —  What  is  sulphur  like  ? 

—  What  is  phosphorus  like  ?  —  What  is  a  match  ?  —  Ex- 
ercises. 

CHAPTER  XIV 

Water 141 

Where  is  water  found  ?  —  What  is  water  like  ?  —  How  does 
water  boil  ?  —  How  is  ice  made  ?  —  How  is  ice  cream  frozen  ? 

—  How   do  bodies   of  water  affect  climate  ?  —  How   does 
water  change  the  earth's  surface  ?  —  Exercises. 

CHAPTER  XV 

Water  Supply  and  Sewerage 152 

Why  do  we  need  so  much  water  ?  —  How  do  cities  get 
their  water  ?  —  How  do  we  get  water  in  the  country  ?  — 
What  is  plumbing  ?  —  What  is  a  pump  ?  —  What  is  a  force 
pump  ?  —  What  are  the  dangers  in  water  ?  —  How  can  we 
get  pure  drinking  water  ?  —  What  is  a  filter  ?  —  Can  a  city 
filter  its  water  ?  —  May  water  be  purified  by  chemicals  ?  — 
What  is  hard  water  ?  —  Exercises. 

CHAPTER  XVI 

Rocks  and  Soil 163 

What  is  the  earth's  crust  ?  —  What  are  the  classes  of 
rocks  ?  —  How  are  stratified  rocks  formed  ?  —  What  are 
fossils  ?  —  How  are  unstratified  rocks  formed  ?  —  What  is 
weathering  ?  —  How  do  plants  cause  weathering  ?  —  How 
does  the  air  aid  weathering  ?  —  How  do  water  and  ice  cause 


CONTENTS  xi 


PAGE 


weathering  ?  —  How  is  our  soil  formed  ?  —  What  is  the 
structure  of  soil  ?  —  Why  must  soil  be  tilled  ?  —  What  is 
irrigation?  —  Do  crops  rob  the  soil?  —  How  can  soil  be  kept 
fertile  ?  -7-  Why  should  crops  be  rotated  ?  —  Exercises. 

CHAPTER  XVII 

Minerals  and  Metals 178 

What  are  minerals  ?  —  Is  iron  necessary  to  man  ?  —  How 
is  iron  found  ?  —  How  is  iron  prepared  ?  —  How  is  lead 
obtained  ?  —  How  is  copper  obtained  ?  —  How  are  gold 
and  silver  found  ?  —  What  is  22-carat  gold  ?  —  How  do 
men  find  precious  stones  ?  —  What  is  coal  ?  —  What  are 
our  building  stones  ?  —  Does  man  ever  make  stones  ?  — 
Exercises. 

PART  IV 
SCIENCE   IN   THE   HOUSEHOLD 

CHAPTER  XVIII 
Acids  and  Alkalies 191 

Do  we  use  science  in  the  home  ?  —  Where  are  acids  found  ? 

—  What  makes  a  compound  an  acid  ?  —  What  are  bases  like  ? 

—  How  can  we  test  for  bases  and  acids  ?  —  How  does  an 
acid  act  with  a  base?  —  Exercises. 

CHAPTER  XIX 

Washing  and  Cleaning 198 

What  are  the  materials  of  clothing  ?  —  How  are  silk  and 
wool  obtained  ?  —  How  is  clothing  washed  ?  —  How  does 
soap  work  ?  —  How  is  soap  made  ?  —  What  is  dry  cleaning  ? 

—  Exercises. 

CHAPTER  XX 

Food 206 

Why  do  we  need  food  ?  —  What  foods  give  us  energy  ?  — 
What  foods  make  us  grow  ?  —  What  are  the  minerals  in 
foods  ?  —  Why  do  we  need  water  in  the  diet  ?  —  How  do  we 
depend  upon  plants  ?  —  Exercises. 


xii  CONTENTS 

CHAPTER  XXI 

PAGE 

The  Cooking  and  Baking  of  Foods       .  ....      214 

Why  do  we  cook  food?  — -  Why  are  foods  cooked  in  boil- 
ing water?  —  What  is  broiling?  —  How  do  we  fry  foods?  — 
What  is  the  baking  of  foods  ?  —  Why  is  baking  powder  used  ? 
—  What  is  yeast  ?  —  How  does  yeast  act  in  making  bread  ? 
—  Exercises. 

CHAPTER  XXII 

The  Preserving  of  Foods 222 

How  do  we  can  and  preserve  foods  ?  —  How  does  drying 
preserve  food  ?  —  How  is  meat  smoked  ?  —  What  are  salting 
and  pickling?  —  How.  does  sugar  preserve  food?  —  What 
are  the  principles  of  canning  ?  —  What  are  the  methods  of 
canning?  —  Does  canning  pay?  —  Canning  as  a  factory 
industry.  —  Do  preservatives  harm  food?  —  Exercises. 

Appendix 231 

Glossary 235 

Index   .  239 


PART   I 
INTRODUCTION 


JUNIOR   SCIENCE 

CHAPTER  I 
BEGINNINGS   OF   SCIENCE 

1.  Some  Questions  to  Think  About.  —  Did  you  ever 
wonder  why  water  runs  down  hill  and  not  upward?  Or 
why  a  kite  flies,  why  trees  shed  their  leaves,  why  plants 
produce  seeds,  why  dew  is  formed,  why  milk  sours,  why 
yeast  raises  bread,  why  the  moon  grows  and  wanes,  why 
the  sun  gives  off  heat?  Did  you  ever  wonder  what  fire, 
sound,  light,  and  electricity  are,  why  we  have  eclipses  of 
the  sun  and  the  moon,  what  lightning  is,  how  soil  is  formed, 
why  grass  is  green,  how  we  are  nourished  by  our  food  ? 

There  seems  to  be  no  end  to  the  questions  you  can  ask 
yourself  regarding  the  objects  you  see  and  what  happens 
to  them.  So  far  as  we  know,  men  have  always  wondered 
about  the  earth  and  the  sky ;  they  seem  always  to  have 
tried  to  find  the  reason  for  the  many  things  that  happen 
in  this  world  of  ours.  To  be  sure,  the  answers  they  first 
gave  would  probably  sound  very  foolish  to  us,  but  grad- 
ually men  were  able  to  give  well-thought-out  and  com- 
mon-sense answers  to  questions  regarding  nature ;  their 
answers  are  what  we  study  in  Science. 

3 


SCIENCE 

2.  Old;   and    New    Answers.     -  You    have    probably 
read   about  some  of  '  f he  strange  ideas  of   men  of   past 
times.     If   you   had   asked,  a   few   centuries   ago,  what 
causes  an  eclipse  of  the  sun,  you  might  have  been  told 
that  a  great  beast  or  spirit  moves  across  the  sky  and 
blots  out  the  sun ;  afterwards  men  saw  that  an  eclipse  of 
the  sun  never  occurs  except  at  the  time  of  "  hew  moon/' 
that  is,   when  the  moon  is  between  the  sun   and   the 
earth  (cf.  §92).     So  they  decided  that  it  is  the  moon, 
not  a  beast  or  spirit,   that  sometimes  comes   exactly 
between  us  and  the  sun. 

We  have  all  read  how  men  made  fun  of  Columbus  because  he  be- 
lieved that  the  earth  is  a  sphere;  the  people  of  his  day  felt  certain 
that  if  the  earth  were  round,  the  people  on  the  other  side  of  it  must 
be  standing  heads  down.  Since  the  days  of  Columbus  we  have  be- 
come used  to  the  idea  that  we  are  living  on  a  great,  round  ball ;  we 
see  that  "  down  "  means  toward  the  earth's  center,  while  "  up  "  means 
away  from  it;  we  are  not  afraid  that  we  may  become  dizzy  from 
standing  topsy  turvy,  nor  that  the  earth  will  in  some  way  lose  its  grip 
apon  us  and  let  us  drop  off  into  space. 

Franklin  helped  us  to  understand  another  mystery  of  nature :  the 
lightning.  No  doubt  many  people  thought  him  foolish,  on  that  June 
day  in  1752,  to  send  up  a  kite  (Fig.  1)  when  a  thunderstorm  was 
coming  on.  But  men  since  that  time  have  honored  Franklin,  because 
his  experiment  showed  that  lightning  is  only  a  great  electric  spark. 
So  we  might  go  on  with  stories  of  how  common-sense  ideas  of  nature 
grew  up  among  men. 

3.  What  is  Science?  —  Columbus  and  Franklin  and 
other  great  discoverers  and  inventors  were  able  to  do 
big  things  for  the  world  because  they  learned  early  to 
notice  common  things  and  to  think  clearly  about  them. 


BEGINNINGS  OF  SCIENCE 


If  we  wish  really  to  know  ourselves,  our  homes,  our 
world,  we  must  do  the  same.  To  learn  science  we,  too, 
must  observe  the  objects  about  us  and  the  changes  that 
take  place  in  them.  We  must  see  them  not  only  with 


FIG.   1.  —  Franklin  raising  his  kite. 

sharp  eyes,  but  with  minds  sharpened  to  question  why 
and  to  work  out  a  sensible  answer.  We  call  a  change  in 
an  object,  such  as  a  fire,  an  eclipse,  or  the  falling  of  a 
stone,  a  phenomenon  ;  the  plural  is  phenomena. 

Think  of  all  we  could  learn  if  we  would  keep  our  eyes 
open  at  home  and  on  our  way  to  and  from  school !  We 
do  not  even  need  to  go  into  the  country  to  learn  about 


6  JUNIOR  SCIENCE 

trees,  shrubs,  and  weeds,  about  insects,  birds,  rocks, 
clouds,  and  the  wind,  or  how  the  ground  is  washed  by 
the  rain.  Suppose  we  really  "  look  into  "  the  kitchen 
and  find  out  what  materials  and  tools  are  used  in  cook- 
ing, baking,  and  cleaning,  and  why  each  is  used ;  what 
"tin"  dishes  are  made  of;  how  such  things  as  can- 
openers,  egg-beaters,  gas  stoves,  faucets,  and  sink  traps 
"  work."  Suppose  we  watch  the  washing  and  ironing 
of  clothes  and  find  out  what  materials  are  used  and 
why ;  how  the  washing  of  woolen  goods  differs  from  that 
of  cotton  ;  why  bluing  is  used ;  why  tubs,  if  of  metal,  are 
of  galvanized  iron,  while  clothes  boilers  are  of  tinned 
copper  and  washboards  of  zinc  ;  why  clothes  dry  so  rapidly 
on  one  day  and  so  slowly  on  another  day. 

There  is  ever  so  much  more  that  we  can  find  out  in  our  homes,  but 
let  home  be  only  the  beginning  of  our  field  of  study.  Let  us  find  some 
way  of  watching  a  painter  at  his  work  and  try  to  learn  what  paint  is 
made  of  and  what  each  part  of  it  is  for.  We  can  also  make  it  a  point 
to  see  the  mason,  the  cement  worker,  the  electrician,  the  carpenter, 
the  plumber,  the  blacksmith,  the  farmer,  and  the  gardener  at  their 
work,  and  can  let  each  of  these  be  our  teacher.  We  shall  find  that 
every  workman  knows  a  great  deal  about  his  art,  or  trade;  after  a 
while  we  may  be  able  to  learn  the  scientific  reasons,  that  is,  the  real, 
common-sense  reasons,  for  what  he  does. 

4.  What  is  an  Experiment?  —  You  have  already  seen 
how  much  we  can  learn  if  we  observe  common  objects 
and  phenomena  closely  and  think  clearly  about  them. 
In  science  we  also  study  by  experiment,  that  is,  we  put 
substances,  or  plants,  or  animals,  under  certain  special 
conditions,  so  as  to  find  out  what  happens  to  them. 


BEGINNINGS  OF  SCIENCE  7 

Thus,  we  put  a  geranium  in  a  dark  room,  so  as  to  learn 
how  it  will  grow  without  light ;  or  we  feed  different 
kinds  of  food  to  a  pig,  in  order  to  find  out  which  will 
fatten  it  the  most  rapidly ;  or  we  put  some  sugar  into  a 
dish  and  heat  it,  to  learn  how  hot  it  is  when  it  chars ; 
or  we  see  how  much  we  can  stretch  a  brass  wire  before  it 
breaks ;  or  we  pass  light  through  a  piece  of  thick  glass, 
to  find  out  how  the  light  will  be  changed.  The  ex- 
periments with  the  geranium,  the  pig,  the  sugar,  the 
brass  wire,  and  the  light  are  really  questions  put  to 
nature.  The  result  of  the  experiment  is  the  answer 
nature  gives  us.  Our  business  is  to  understand  the 
answer  correctly. 

5.  Why  Study  Science  ?  —  Science  is  the  foundation 
of  our  modern  life,  of  its  manufacturing  industries,  its 
agriculture,  its  steamship,  railroad,  and  electric  lines,  of 
its  telephone,  telegraph,  and  wireless  service.  To  science 
the  farm  owes  its  modern  machinery,  its  better  and  larger 
crops  of  grain,  its  fine  stock  and  poultry,  its  more  abun- 
dant fruit ;  to  science  the  up-to-date  city  house  and  school 
building  owe  their  cleanliness,  light,  fresh  air,  and  con- 
veniences. We  should  study  science,  then,  not  merely 
to  "  observe  phenomena, "  but  to  understand  the  ways 
of  the  community  in  which  we  live. 

We  may  think  that  the  comforts  we  now  enjoy  have 
always  been  here;  our  great-grandparents,  if  they  were 
living,  could  tell  a  different  story.  They  would  tell  of  a 
time  when  such  common  things  as  glass  and  soap  were 
expensive  and  not  easy  to  get,  when  houses  had  no 
running  water,  when  it  was  hard  to  provide  heat  and 


8 


JUNIOR  SCIENCE 


light,  when  cloth  was  woven  at  home,  and  when  food 
canned  in  "  tin  "  was  unknown. 

A  little  further  back  in  time,  even  the  wealthy  could  not 
have  the  commonest  of  modern  comforts.  Their  houses 
were  full  of  drafts  and  were  dark  and  dirty ;  news  came 
slowly ;  books  were  scarce  and  expensive ;  traveling  was 
hard  and  dangerous.  The  farming  of  those  days  was  very 

difficult,  for  farm  tools 
were  crude  and  farm 
machinery  was  un- 
known (Fig.  2).  When 
we  compare  this  con- 
dition of  things  with 
our  modern  ways,  with 
the  rapid  transporta- 
tion of  people,  freight, 
and  news,  with  cheap 
books  and  free  libra- 
ries, with  the  care  of 
public  health,  with 
scientific  agriculture, 
we  get  some  idea  of 
what  science  means  to  the  world. 

But  all  this  study  of  science  will  mean  little  to  us 
unless  we  apply  it  to  ourselves  and  to  our  way  of  living. 
We  must  also  learn  about  these  bodies  of  ours,  so  that 
we  may  know  what  things  will  bring  us  health  and  power 
and  what  will  make  us  weak  and  useless.  No  amount  of 
knowledge  will  help  us  much,  if  we  do  not  have  proper 
food  and  clothing,  vigorous  exercise,  abundant  sleep, 


(Copyright,  International  Stereograph  Co.) 
FIG.  2.  —  How  an  Egyptian  does  his  plowing. 


BEGINNINGS   OF   SCIENCE  9 

and  strong  habits  of  cleanliness  and  good  conduct. 
Science  shows  us,  as  nothing  else  can,  how  to  have  "  a 
sound  mind  in  a  sound  body  J ;  we  should  study  it  to 
learn  how  to  live  long  and  useful  lives. 

6.  What  We  Have  Learned.  —  Science  begins  with  common-sense 
answers  to  questions  regarding  nature. 

Nature  includes  objects  and  phenomena. 

Phenomena  are  changes,  or  happenings,  in  objects. 

The  objects  and  phenomena  we  study  are:  (1)  those  of  nature; 
(2)  those  of  home  industries  and  the  common  occupations ;  (3)  those 
of  experiments. 

To  experiment  is  to  question  nature  with  a  purpose. 

7.  Exercises. — - 1.   What  are  the  proofs  that  the  earth  is  round, 
and  not  flat  ?     Who  first  sailed  around  it  ? 

2.  What  is  the  diameter  of  the  earth?      Of  the  moon?      How  far 
is  the  moon  from  the  earth?     (Consult  Chapter  XI.) 

3.  Make  a  list  of  some  of  the  great  inventions,  with  their  dates 
and  the  names  of  the  inventors. 

4.  Name  some  of  the  important  scientific  discoveries  of  the  last 
century. 

5.  Make  a  list  of  the  tools  and  apparatus  used  in  your  kitchen, 
for  cooking,  baking,  and  cleaning. 

6.  Make  a  list  of  the  different  substances  used  in  your  kitchen  and 
laundry. 

7.  Give  the  names  and  uses  of  the  most  important  tools  and 
machines  used  by  carpenters ;  by  gardeners ;  by  up-to-date  farmers. 

8.  Make  a  list  of  the  different  kinds  of  materials  used  in  the  build- 
ing of  a  house. 

9.  Name  the  different  methods  used  for  carrying  (and  lifting) 
passengers  and  for  sending  freight  and  news. 


PART   II 

THE   ATMOSPHERE   AND  ITS   RELATION 

TO   MAN 


CHAPTER  II 
AIR 

8.  What  is  Air  Like  ?  —  One  of  the  hard   things  for 
man  to  understand  was  the  air.     It  fanned  his  cheek, 
turned  his  windmills,  and  drove  his  ships,  but  he  could 
not  find  out  much  about  it  until  a  little  over  a  hundred 
years  ago.     We  can  see  why  this  was  true.     Air  is  in- 
visible to  us,  except  when  we  see  its  quivering  motion 
over  a  hot  stove  or  on  a  hot  day  in  summer.      What  man 
could  not  see,  he  found  it  hard  to  handle  and  to  under- 
stand.    Thus,  when  he  used  up  some  of  the  air,  he  did 
not  know  that  he  had  done  so,  because  more  air  rushed 
in  from  all  sides  to  fill  the  empty  space.     Observe  how 
the  surrounding  water  rushes  in  when  we  dip  some  of  it 
out  of  a  tub  or  pail ;  air  would  rush  in  in  the  same  way. 
When  men  grew  used  to  this  idea,  they  did  not  try  to 
study  all  the  air  at  once,  but  they  took  vessels  of  air, 
such  as  tanks  or  bottles,  stoppered  them  in  some  way, 
and  then  studied  this  enclosed  portion  of  air  by  itself. 
In  this  way  they  learned  a  great  deal  more  about  the  air. 

9.  Does  Air  Take  Up  Room  ?  —  Have  you  ever  thought, 
as  you  filled  a  glass  with  water  from  a  pitcher  or  faucet, 
whether  anything  was  flowing  out  of  the  glass  while  the 
water  flowed  in?     Have  you  ever  poured  water  out  of  a 
small-mouth  bottle?     Try  it  and  see  whether  anything 

13 


14 


JUNIOR  SCIENCE 


happens  which  shows  that  something  goes  into  the  bottle 
as  water  flows  out. 

Suppose  we  push  a  glass,  held  upside  down,  into  a 

deep  dish  of  water ;   does  the  water  rise  up 

to  fill  the  glass?     Why? 

Let  us  perform  the  following  experiment  (Fig.  3) : 
Put  a  funnel  stem  loosely  into  a  small-mouth  bottle, 
such  as  a  ketchup  or  vinegar  bottle,  and  quickly  fill 
the  funnel  with  water.     Does  the  water  run  in  as  a 
stream,  or  by  spurts  ?     Now  fit  the  funnel  stem  tightly 
into  the  mouth  of  the  bottle.     You  can  use  a  one-hole 
stopper  for  this  purpose,  or  you  can  wind  around  the 
FIG.  3.  -  -   stem  a  strip  of  wet  muslin,  about  an  inch  wide,  until 

mn1  intoWtMs   the  Joint  *  i[&hi'     Finally,  fill  the  funnel  rapidly  with 

bottle    in    a   water.    How  does  the  water  run  in  now?     Why? 

stream,  or  by        Carry  out  another  experiment  (Fig.  4) : 

Fill  a  bottle  with  water  and  close  the  mouth  of  the 

bottle  tightly  with  your  hand ;  then  turn  the  bottle  upside  down  in  a 

pan  of  water.    If  the  mouth  of 

the  bottle  is  under  water,  you 

can  remove  your  hand  without 

the   water  falling  out.    If  you 

then  blow  air   into  the   bottle 

through  a  bent   tube,  you   can 

collect  the  air  in  the  bottle ;  for 

as  the  air  bubbles  rise  into  the 

bottle,  they  push  the  water  out. 

In  this  way  we  can  collect  a  gas 

"  over  water. " 

FIG.  4.  —  Collecting   the    air   of    your 
T,  .  breath  "over  water." 

From  these  experiments 

we  can  see  that  air  takes  up  room,  or  occupies  space, 
just  as  water  does.     If  we  want  to  pour  water  into  a 


AIR  15 

vessel,  we  must  give  the  air  a  way  of  getting  out ;  if  we 
want  to  pour  the  water  out  of  a  vessel,  we  must  let  the 
air  go  in  to  take  its  place. 

10.   Does  Air  Have  Weight?  —  When  we  have  grown 
used  to  the  idea  that  air  fills  vessels  that  we  think  of  as 
:(  empty/7  we  are  ready  to  believe  that  air  has  weight. 
How  can  we  find  out  if  this  is 
true? 

If  we  wish  to  get  the  weight 
of  a  cupful  of  water  (Fig.  5), 
we  first  weigh  the  "  empty " 
cup ;  then  we  fill  the  cup  with 
water  and  get  the  weight  of  the  FlG'  5'  ~  *Jg£  laboratory 
cup  and  water  together.  By 

subtracting  the  weight  of  the  cup  from  the  weight  of  the 
cup  and  water,  we  get  the  weight  of  the  water  alone. 
We  write  down  the  results  in  this  way : 

Weight  of  cup  and  water  = .  .  .  .  ounces. 

Weight  of  cup  alone  = .  .  .  .  ounces. 

Weight  of  water  alone  = .  .  .  .  ounces. 

You  may  have  seen  this  method  used  when  you  have 
bought  butter  in  a  crock  or  honey  in  a  pail.  The  weight 
of  the  butter  or  honey  alone  is  spoken  of  as  the  "  net  " 
weight,  while  the  weight  of  the  material  and  the  con- 
tainer together  is  the  "  gross  "  weight. 

When  we  weigh  an  "  empty  "  cup,  crock,  or  pail,  we 
make  no  account  of  the  air  which  it  contains.  But 
when  we  try  to  find  out  whether  or  not  air  has  weight, 
we  must  first  get  the  weight  of  a  vessel  which  is  really 


10 


JUNIOR  SCIENCE 


empty,  that  is,  without  even  air  in  it.  One  way  to  do 
this  is  to  attach  the  vessel,  such  as  a  flask  (Fig.  6),  by 
means  of  rubber  tubing,  to  an  air  pump  and  then  to  re- 
move all  the  air  we  possibly  can.  Then,  while  the  flask 
is  still  attached  to  the  air  pump,  we  close  the  stopper  in 
the  glass  tubing.  We  can  now  weigh  the  flask  really 
empty  ;  then  we  open  the  stopper,  let  air  enter,  and  weigh 
the  flask  again.  The  flask  and  air  together 
weigh  more  than  the  empty  flask,  so  air  must 
have  weight. 

11.  Is  Ak  Matter?  —  Since  air  takes  up 
room  and  has  weight,  it  is  a  form  of  matter, 
or  a  substance,  just  as  water  and  sugar  are 
substances. 

One  cubic  foot  of  air  ordinarily  weighs 
about  1 1  ounces ;  how  can  we  find  out  how 
much  the  air  of  your  schoolroom  weighs  ? 


FIG.  6.  — 
A  flask  from 
which  we  can 
remove  the 
air. 


Suppose  that  the  room  is  24  feet  long,  20  feet  wide, 
and  10  feet  high.  The  volume,  in  cubic  feet,  will  be 
24X20X10,  or  4800  cubic  feet.  Since  1  cubic  foot  of 
air  weighs  about  1J  ounces,  the  air  of  the  room  must  weigh  about 
4800  Xli,  or  6000  ounces.  To  get  the  weight  hi  pounds  we  divide 
6000  ounces  by  16.  So  the  schoolroom  holds  about  375  pounds  of  air. 

Measure  the  living-room  of  your  house  and  find  the 
volume  and  weight  of  the  air  it  holds. 

12.  How  Do  Heating  and  .Cooling  Affect  Air?  —  Sup- 
pose we  set  an  "  empty  "  flask  upside  down  in  a  shallow 
dish  of  water  (Fig.  7)  and  carefully  heat  the  flask  with  a 
burner,  or  pour  hot  water  over  it ;  what  happens  ?  We 
can  also  try  warming  the  flask  by  means  of  our  hands. 


AIR 


17 


As  the  air  in  the  flask  is  warmed,  it  expands,  so  that  its 
volume  is  too  great  for  the  flask,  and  some  of  it  escapes 
through  the  water.  If  we 
pour  cold  water  over  a 
second  flask  of  air,  the  air 
contracts  in  volume.  Since 
the  outside  air  cannot  .get 
into  the  flask,  water  is  forced 
up  instead.  Think  of  some 
cases  you  have  seen  in  which 
air  expands  and  contracts. 
13.  Can  Air  Be  Com- 


FIG.  7.  —  Heating  the  air  expands 


it,  while  cooling  makes  it  shrink,  or 

pressed?  — We  saw  in  the    contract 

last  section  that  if  air  is  cooled,  it  shrinks  in  volume. 
This  is  the  same  as  saying  that  it  occupies 
a  smaller  space.  We  can  also  force  air  to 
occupy  a  smaller  space  if  we  increase  the 
pressure  upon  it.  Thus,  a  popgun  is  a  tube 
having  one  end  closed  by  a  cork  and  the 
other  end  closed  by  a  piston.  As  we  force 
the  piston  into  the  tube,  we  compress  the 
air  inside.  Finally  its  pressure  becomes  great 
enough  to  force  the  cork  out  with  a  "  pop." 
We  can  see  how  the  pressure  of  water 
compresses  air,  if  we  put  a  glass  of  air,  upside 
down,  under  water.  The  deeper  the  water, 
the  smaller  the  volume  of  the  air  will  become. 
We  can  see  this  better  if  we  fasten  a  glass 

pressed  by  the    viai  or  flask  (pig.  8)  to  a  rod  of  glass  or  metal 

pressure  of  the  .     . 

water  in  the  jar.    and  put  it  into  a  deep  vessel  of  water. 


FIG.  8.  — 
The  air  in  the 
vial  is  com- 


18 


JUNIOR  SCIENCE 


f\ 


The  apparatus  of  Fig.  9  also  shows  how,  by  increasing  the  pressure, 
we  decrease  the  volume  of  a  gas.  If  we  begin  with  a  certain  volume 
of  air  in  the  closed,  shorter  arm  of  the  bent 
tube,  and  add  portions  of  water  or  mercury 
(quicksilver)  to  the  longer  arm,  the  air  will  be 
forced  into  a  smaller  and  smaller  space.  Mer- 
cury is  used,  because  it  is  so  much  heavier  than 
water;  a  column  of  mercury  1  inch  high  will 
compress  the  air  as  much  as  a  column  of  water 
13.6  inches  high,  because  mercury  is  13.6  times 
as  heavy  as  water. 

14.   For  What  Can  Compressed  Air 
Be  Used?  —  Have  you  ever  thought 
of  some  of  the  important  uses  man  has 
made  of  compressed  air?     To  pack  air 
FIG.  9.  —  The  air  in    into  a  smaller  space  we  commonly  use 

the  closed  arm  of   the 


V 


L 


tube  is  compressed  by 
the  weight  of  the  mer- 
cury in  the  longer  arm. 


a  compression  pump.  The 
bicycle  and  automobile 
pumps  (Fig.  10)  are  the 
most  common  of  the  compression  pumps; 
they  are  used  to  crowd  a  great  deal  of  air 
into  the  tire.  The  compressed  air,  as  well 
as  the  rubber  tire,  acts  as  an  elastic  cushion 
and  protects  the  car  from  jolts.  We  can 
also  use  a  bicycle  pump  to  crowd  air  into  The*0  bicycle 
a  basketball  or  football.  PumP  com- 

presses  a  great 

How  do  you  suppose  men  lay  the  founda-    deal  of  air  into 
tions  of  bridges  in  the  bottom  of  a  river,  or    the  * 
do  other  work  under  water?     We  learned  in  the   last 
section  that  if  a  vessel  of   air  is   pushed,  mouth  down- 
ward, under  water,  the  pressure  of  the  water  compresses 


To  bicyi 


AIR 


19 


the  air.  If  we  are  to  keep  the  vessel  entirely  full  of 
air,  we  must  force  a  supply  of  air  into  the  vessel.  This 
is  what  is  done  in  the  diving  bell  (Fig.  11),  in  which 
men  work  under  water.  Compressed  air  is  forced  into 
the  "  bell  "  at  such  a  pressure  that  it  keeps  the  water 
from  rushing  in  and  furnishes  fresh  air  for  the  diver. 
The  air  is  kept  flowing,  so  that 
it  bubbles  out  around  the 
edge  of  the  bell. 

A  caisson  is  a  diving  bell  which 
men  use  in  placing  the  foundations  of 
large  buildings,  when  water  rushes 
into  the  excavations  (cf.  §  133). 

You  would  not  think  that  a 
submarine  boat  is  a  device  for  using 
compressed  air,  yet  this  is  so.  It  has 
compartments,  or  spaces,  which  can 
be  filled  with  either  water  or  com- 
pressed air.  When  water  is  allowed 
to  push  the  air  out  of  these  spaces, 
the  boat  as  a  whole  is  heavier  and 

sinks  under  water;  when  compressed  air  is  used  to  force  the  water 
out  of  the  spaces,  the  boat  rises  to  the  surface.  The  compressed  air 
apparatus  also  keeps  the  sailors  supplied  with  air  for  breathing. 

There  are  many  other  inventions  that  use  compressed  air.  Have 
you  ever  heard  the  rapid  pounding  of  the  pneumatic  hammer  on  a 
steel  bridge  or  building?  It  is  used  to  rivet  together  large  pieces  of 
steel,  and  increases  greatly  the  speed  with  which  steel  structures  can 
be  built. 

The  air  brake,  invented  by  George  Westinghouse,  is  another  im- 
portant piece  of  apparatus  that  uses  compressed  air.  It  sets  the 
brakes  against  the  wheels  of  railroad  cars  and  stops  the  train.  The 
air  is  compressed  and  stored  in  the  locomotive. 


Flo.  11.  —  Air  is  kept  flowing 
through  the  bell,  so  that  the  work- 
man can  lay  a  foundation  upon 
the  bottom. 


20  JUNIOR  SCIENCE 

A  sand  blast  is  a  current  of  air  set  free  from  pressure  and  carrying 
sharp  sand  with  great  speed.  It  is  used  to  roughen  the  surface  of 
glass,  producing  "  ground  glass."  The  sand  particles  chip  the  sur- 
face. The  wind  of  a  sandy  desert  is  a  natural  sand  blast ;  it  not  only 
roughens  window  glass,  but  wears  away  the  surface  of  rocks  (cf.  §  151). 

15.  Exercises.  —  1.  Is  it  easy  to  get  ketchup  out  of  a  small-mouth 
bottle  ?  How  do  you  do  it  ?  Why  ? 

2.  How  do  we  get  machine  oil  out  of  its  can?     Why? 

3.  Why  is  there  a  vent,  or  hole,  near  the  top  of  a  vinegar  or  kerosene 
barrel?     Why  is  there  one  in  a  steam  radiator? 

4.  Examine  a  kerosene  or  gasoline  can.     How  does  the  liquid  come 
out  of  the  spout  when  the  top  of  the  can  is  closed?     How,  when  the 
top  is  open?    Why? 

5.  If  you  bring  an  inflated  toy  balloon  from  the  cold,  outer  air  into 
a  warm  room,  what  will  happen  to  it?     Why? 

6.  Set  an  "  empty  "  glass,  mouth  down,  into  a  saucer  or  basin  of 
hot  water;  what  happens,  and  why?     Have  you  ever  noticed   any 
phenomenon  like  this  in  the  rinsing  of  dishes  with  hot  water? 

7.  Suppose  you  balance  two  dry,  "  empty  "  flasks  or  tomato  cans 
on  the  two  pans  of  the  scales,  and  then  heat  one  of  the  flasks,  or  cans, 
and  put  it  back  on  the  scales ;  what  will  happen,  and  why? 

8.  Do  you  think  the  gas  in  an  inflated  toy  balloon  is  under  pressure  ? 
Why? 

9.  Suppose  that  the  inside  space  of  a  basketball  holds  £  of  a  cubic 
foot.     How  much  does  this  volume  of  air  weigh?     Suppose  that  three 
times  this  volume  of  air  is  packed  into  the  ball,  what  does  the  air  in 
the  ball  weigh? 


CHAPTER   III 
PRESSURE   OF  THE  ATMOSPHERE 

16.   Does   the  Atmosphere   Have  Pressure?  —  If  we 

were  living  at  the  bottom  of  an  ocean  of  water,  the  weight 
of  the  water  above  us  would  cause  a  great  pressure  upon 
our  bodies  and  upon  all  the  objects  in  the  water.  Is  the 
same  true  of  an  ocean  of  air?  Let  us  perform  a  few  ex- 
periments to  find  out. 

(a)  Look  back  at  §  9,  Fig.  4.  Why  does  not  the  water  fall  out  of 
the  bottle  that  is  set,  upside  down,  in  the  pan  of  water? 

(6)  Fill  a  drinking  glass  or  a  large-mouth  bottle  completely  with 
water,  close  the  mouth  of  the  vessel  entirely  with  a  wet  piece  of  card- 
board or  stiff  paper ;  a  stiff  envelope  will  do.  Now  hold  the  cover- 
ing in  place  with  your  hand,  turn  the  vessel  upside  down,  and  remove 
your  hand.  Why  does  not  the  water  fall  out?  In  what  direction 
does  the  atmosphere  exert  pressure  in  this  case? 

(c)  Hold  a  clean  glass  vial  or  other  small-mouth  bottle  between 
your  lips  and  remove  as  much  as  possible  of  the  air  by  suction.     Then, 
before  the  air  reenters,  close  the   mouth  of  the  vial  or  bottle  with 
your  tongue  or  the  inside  of  your  lips  or  cheek.     What  evidence  do 
you  get  of  the  pressure  of  the  atmosphere?     What  happens  when 
you  pull  the  bottle  away? 

(d)  Over  the  mouth  of  a  clay  pipe  tie  tightly  a  piece  of  thin  sheet 
rubber  and  then,  by  suction  through  the  stem,  remove  some  of  the 
air.     Explain  what  happens.     Does  this  show  anything  of  air  pressure  ? 

If  your  laboratory  has  an  air  pump,  perform  the  same  experiment 
as  shown  in  Fig.  12. 

(e)  Blow  a  paper  bag  full  of  air. 

21 


22 


JUNIOR  SCIENCE 


The  pressure  of  the  air  inside  and  outside  the  bag  will  then  be  the 
same.  Now  make  the  mouth  of  the  bag  small  and  remove  the  air  by 
suction.  Why  does  the  bag  collapse? 

Can  you  tell  why  you  can  drink  lemonade  or  soda  water 
through  a  straw  ? 

Do  any  of  these  experiments  show  that  the  atmosphere's 
pressure  pushes  upwards?  Downwards?  Sidewise? 

17.   Can    the    Atmos- 

Iphere's  Pressure  Be 
Measured  ?  Suppose 
that  you  had  a  tube  or 
pipe  10,  20,  30,  or  40 
feet  long  and  that  your 
lungs  were  strong  enough, 
could  you,  by  suction, 

£[~~  CT"1F^3\     ra*se    a    l^11^    such    as 

-~^^"-^fe"-^fe  \    water  or  lemonade,  up  to 

"~^—  your  mouth  ?  Your  lungs 
are  not  strong  enough, 
but  you  could  use  a  suc- 
tion, or  lift,  pump  for  the 
purpose.  This  is  just  what  we  usually  do  when  we  pump 
water  from  a  well  or  cistern. 

Nearly  300  years  ago  a  landowner  in  Italy  was  trying 
to  raise  water  from  a  well.  No  pump  he  could  get  would 
raise  the  water  more  than  about  34  feet.  He  asked  the 
scientist  Galileo  (pronounced  Gal-i-le'6)  to  tell  him  why ; 
but  Galileo  did  not  know.  Torricelli  (pronounced  Tor- 
rf-tchell'y),  a  pupil  of  Galileo,  gave  the  answer  in  1643. 
He  believed  that  water  rose  into  a  pump  because  the 


FIG.  12.  —  As  the  air  is  removed  from 
the  bell-shaped  jar  by  the  air  pump,  the 
pressure  of  the  outside  air  forces  the  sheet 
rubber  into  the  jar. 


PRESSURE  OF    THE   ATMOSPHERE 


23 


atmosphere's  pressure  forced  it  up.  He  said  to  himself 
that  if  the  pressure  of  the  atmosphere  was  just  great 
enough  to  push  up  a  column  of  water  34  feet,  it  could  not 
push  up  a  heavier  liquid  to  so  great  a  height.  He  decided 
to  try  mercury,  which  is  13.6  times  as  heavy  as  water. 
If  Torricelli's  guess  was  correct,  the  air  ought  to  be  able 
to  hold  up  a  column  of  mercury  only 
34- 13.6,  or  about  2,5  feet  high.  This 
would  be  about  30  inches. 

18.  The  Barometer.  —  To  test  his 
guess,  Torricelli  used  a  straight  glass 
tube  about  3  feet  long  (Fig.  13)  and 
closed  at  one  end.  He  filled  the  tube 
entirely  with  mercury,  closed  the 
open  end  with  his  finger,  and  turned 
the  tube  upside  down,  so  that  its  open 
end  was  below  the  surface  of  some 
mercury  in  a  dish.  When  he  removed 
his  finger,  some  of  the  mercury  ran 
down  into  the  dish,  but  not  all.  It 
stopped  when  the  column  was  about 
30  inches  high.  So  Torricelli's  guess  was  correct.  The 
space  above  the  mercury  did  not  contain  air ;  we  call  it 
a  vacuum,  which  means  empty  space.  Torricelli's  appa- 
ratus is  called  a  barometer. 

If  the  opening  of  a  barometer  tube  has  an  area  of  1 
square  inch,  the  mercury  column  30  inches  high  weighs 
14.7  pounds.  This  is  the  reason  why  we  say  that  the  air 
pressure  on  every  square  inch  of  surface  is  about  15 
pounds. 


FIG.  13.  —  A  barom- 
eter. The  pressure  of  the 
atmosphere  holds  up  the 
column  of  mercury. 


24 


JUNIOR  SCIENCE 


Height 

n  miles 

35 


CB.-xr.  ht 


inches 
l^DOO 


19.  Is  the  Atmosphere's  Pressure  Always  the  Same? 
-  If  we  examine  a  barometer  frequently,  we  shall  find 
that  the  height  of  the  mercury  column  is  not  always  the 
same;  it  varies  from  day  to  day  and  sometimes  even 
from  hour  to  hour.  These  changes  in  the  "  barometer 
height,"  as  it  is  called,  are  caused  by  changes  in  the 
atmosphere's  pressure.  A  study  of  these  changes  is  of 

great  importance  to  the 
weather  observer,  for  they 
help  him  to  foretell  changes 
of  weather.  How  he  does 
this  we  shall  learn  later 
(cf.  §81). 

What  do  you  think  would 
be  the  effect  of  carrying  a 
barometer  down  into  a 
deep  mine  or  up  a  moun- 
tain? At  the  bottom  of 
a  haystack  the  hay  is  more 
compact  than  at  the  middle 
or  the  top,  because  all 
the  hay  above  is  pressing 
upon  that  at  the  bottom.  The  same  would  be  true 
of  a  pile  of  sofa  pillows  or  of  any  other  material  that 
is  easily  compressed.  Is  this  true  of  air?  If  it  is,  then 
the  pressure  should  become  greater  if  we  go  down  into 
a  mine,  and  should  grow  less  if  we  go  to  the  top  of  a 
high  building,  or  up  a  mountain.  This  has  been  found 
to  be  true  (Fig.  14).  At  the  height  of  4  miles  above  sea 
level  the  barometer  height  is  about  15  inches ;  at  about 


FIG.  14.  —  The  balloon  and  the  air- 
plane are  still  in  the  lower  part  of  the 
ocean  of  air. 


PRESSURE  OF   THE   ATMOSPHERE  25 

7  miles  some  aeronauts  found  it  to  be  only  7  inches. 
They  had  thus  left  f  of  the  air  behind  them. 

The  pressure  of  the  blood  in  our  bodies  is  about  17  pounds  to  the 
square  inch;  hence  there  is  danger  of  hemorrhage,  or  bursting  of  the 
blood  vessels,  when  the  atmosphere's  pressure  suddenly  becomes  loo 
small.  So  it  happens  that  many  persons  have  nosebleed  when  they 
are  carried  quickly  up  a  mountain. 

The  barometer  column  falls  about  an  inch  for  every 
900  feet  we  ascend  above  sea  level ;  what  would  its  height 
be  at  an  elevation  of  1800  feet?  Of  4500  feet? 

20.  Exercises. —  1.  If  your  body  has  an  area  of  2000  square 
inches  and  the  atmosphere's  pressure  upon  it  is  15  pounds  for  every 
square  inch,  your  body  must  support  a  pressure  of  30,000  pounds. 
Why  do  you  not  feel  so  great  a  pressure? 

2.  When  the  cover  of  a  Mason  jar  is  hard  to  remove,  we  some- 
times push  a  knife  blade  under  the  edge  of  the  cover  until  we  hear  a 
hissing  noise.     What  causes  the  noise?     Why  is  it  easier  afterwards 
to  remove  the  cover? 

3.  Alcohol  is  only  f  as  heavy  as  water ;  would  a  barometer  column 
consisting  of  alcohol  be  higher  or  lower  than  one  made  of  water? 

4.  Why  is  mercury  used  in  the  barometer  instead  of  water  or  alcohol 
or  any  other  liquid? 

5.  How  could  a  barometer  be  used  to  tell  the  height  of  a  mountain 
top  above  sea  level? 

6.  Can  you  think  of  any  reason  why  the  atmosphere's  pressure 
should  vary  from  day  to  day? 

7.  Could  you  prove,  by  the  use  of  a  clay  pipe  with  sheet  rubber 
tied  ovrr  the  bowl,  that  the  air  presses  hi  all  directions?     Try  it. 


CHAPTER  IV 
FIRE 

21.  What  Does  Fire  Mean  to  Us?  — What  a  number 
of  pictures  come  to  our  minds  as  we  hear  the  word  "  Fire  "  ! 
Perhaps  you  think  first  of  the  fire  that  destroys  some 
house,  of  the  uncontrolled  prairie  fire  and  forest  fire,  of 
the  destructive  fires  in  coal  mines  and  petroleum  wells,  of 
the  great  conflagrations  that  have  swept  over  cities  like 
Rome,  London,  Moscow,  Chicago,  Boston,  and  San 
Francisco.  We  ought  also  to  think  of  the  quiet  fires 
of  the  home :  a  burning  match,  burning  wood  or  coal  in 
the  open  fireplace  or  in  the  stove,  the  gas  jet  and  gas 
stove,  the  flame  of  a  candle,  the  kerosene  lamp,  the 
furnace  fire.  We  think,  too,  of  the  great  fires  of  industry 
and  commerce :  the  blast  furnace,  that  gives  us  iron ; 
the  copper,  zinc,  and  lead  smelters  in  which,  by  the  aid 
of  fire,  these  metals  are  prepared  for  our  use  ;  the  furnace 
fires  that  produce  the  steam  of  the  locomotive  and  steam- 
ship. Then,  too,  we  think  of  the  joyous  bonfire  of  our 
celebrations  and  of  the  camp  fire  over  which  we  cook  our 
picnic  meal. 

It  is  true  that  fire  destroys  many  precious  lives  every 
year  and  enormous  sums  in  property,  yet  without  it 
man  would  be  poor  indeed.  A  proverb  says :  "  Fire  is 

26 


FIRE 


27 


a  good  servant,  but  a  bad  master. " 
same  idea  when  he  says : 


The  poet  has  the 


FIG.    15.  —  Kindling    fire    by 
means  of  a  flint-and-steel. 


"  How  kindly  is  the  fire's  might, 
When  tamed  by  man  and  watched  aright." 

What  is  fire  and  how  did  man  come  to  use  it  ? 

22.  How  Are  Fires  Started?  —  How  do  you  suppose 
man  ever  learned  to  start  a  fire?  Nowadays  we  do  this 
in  a  very  matter-of-fact  way. 
We  strike  a  match  ;  its  tip  bursts 
into  flame ;  then  the  match  stick 
burns  and  we  use  its  flame  to 
kindle  our  fire.  But  suppose  we 
were  off  in  the  woods  or  the 
mountains,  without  matches ; 
how  could  we  kindle  a  fire  then? 

A  hundred  years  ago  there  were 
no  matches ;  men  lighted  their  fires  by  means  of  a  flint-and- 
steel.  That  is,  they  struck  a  piece  of  flint  (a  kind  of  rock) 
with  a  short  bar  of  steel  and  produced  hot  sparks.  They 
caught  the  sparks  in  some  tinder  and  thus  set  the  tinder 
on  fire.  We  often  see  such  sparks  when  a  horse's  hoofs 
strike  a  stone  pavement.  The  tinder  consisted  of  dried 
moss,  bark,  pitch,  or  some  other  substance  that  was 
easily  set  on  fire. 

Our  forefathers  did  not  use  the  flint-and-steel  every  time  they 
wanted  a  fire,  but  saved  the  hot  coals  each  evening  for  the  next  day's 
fire.  If  the  coals  "  went  out/'  as  they  sometimes  did,  some  one 
(usually  a  child)  had  to  go  out  in  the  frosty  morning  to  "  borrow  fire  " 
of  a  neighbor.  The  glowing  coals  were  carried  in  little  covered  iron 
pails  or  kettles. 


28 


JUNIOR  SCIENCE 


But  the  flint-and-steel  was  not  the  earliest  way  of  making  fire. 
At  a  still  earlier  time  men  started  their  fires  by  rubbing  one  piece  of 
wood  against  another,  until  the  wood,  or  some  tinder  placed  near  it, 

was  heated  to  the  kindling  tem- 
perature. Some  barbarous 
peoples  do  this  today  (see 
Fig.  16). 

23.  How  Does  a  Fire 
Burn  ?  —  Watch  a  fire  and 
see  how  the  flame  or  glow 
travels  from  one  part  of 
the  burning  body  to  an- 
other. We  see  this  in  the 
burning  of  an  incense 
stick,  a  match,  or  a  stick 
of  wood,  as  well  as  in  the 
burning  of  a  house  or  a 
city  block.  The  part  al- 
ready afire  heats  up  the 
part  next  to  it  to  the 
"  point  of  burning/ '  or 
kindling  temperature. 

A  number  of  other 
things  happen  in  a  fire.  There  is  usually  a  flame, 
which  gives  off  light.  We  use  lamps  for  the  light  of 
their  flames.  Lincoln  learned  to  read  by  the  light 
of  a  burning  pine  knot.  A  third  thing  about  a  fire 
is  that  it  gives  off  heat;  a  fourth,  that  there  is 
usually  some  smoke.  A  fifth  thing  is  that  after  solid 
fuels,  like  coal  and  wood,  no  longer  burn  with  a  flame, 


(Copyright,  1912,  by  1 


FIG.  16.  —  How  a  Batua  of  the  Congo 
Free  State  kindles  his  fire  by  turning  a 
drill  rapidly  between  his  hands. 


FIRE  29 

they  burn  with  a  glow.  Finally,  when  the  coal  or  wood 
is  entirely  through  burning,  gray  ashes  remain.  Many 
substances  do  not  seem  to  burn  at  all ;  such  are  the  iron 
of  a  stove  and  the  bricks  of  a  fireplace.  Why  does  not 
the  nail  in  a  stick  of  wood  burn  up  with  the  wood  ? 

24.  Experiments  with  Burning.  —  In  order  to  find  out 
more  about  burning,  or  fire,  let  us  carry  out  a  few  ex- 
periments. First  we  must  have  a  bottle  and  a  cork  to 
close  it,  also  a  pine  splinter  that  can  be 
fastened  into  the  under  side  of  the  cork 
(Fig.  17).  Let  us  light  the  splinter  and 
hold  it  in  the  bottle,  and  press  the  stopper 
into  the  bottle's  mouth.  At  first  the  flame 
burns  brightly,  then  faintly;  finally  it 
"  goes  out."  Suppose  we  remove  the  cork, 
relight  the  splinter,  and  thrust  the  splinter  iighJed  splint^ 
once  more  into  the  bottle.  The  splinter  bums  for  a  time 

.,,  ,  T-,  ..  .  in  the  inclosed 

will  not  burn.  Except,  possibly,  for  a  little  air  of  the  bottle 
smoke,  the  inside  of  the  bottle  looks  just  ^, then  "goes 
as  it  did  before  we  burned  the  wood  in  it. 

Let  us  remove  the  splinter,  fill  the  bottle  entirely  with 
water,  pour  out  the  water,  and  put  the  burning  splinter 
back  into  the  bottle.  What  happens?  The  splinter 
burns  once  more.  What  did  the  water  force  out  of  the 
bottle?  The  used,  spent  air.  What  entered  the  bottle 
when  we  poured  the  water  out?  Fresh  air.  The  ex- 
periment shows  that  burning  wood  spoils  the  air  for 
further  burning  and  that  we  must  provide  fresh  supplies 
of  air,  if  burning  is  to  go  on.  The  same  is  true  of  all 
ordinary  burning. 


30 


JUNIOR  SCIENCE 


We  can  perform  the  same  experiment  with  a  burning  candle.  The 
candle  should  be  a  short  one  and  fastened  by  means  of  a  stiff  wire 
to  the  cork,  so  that  the  candle  may  be  held  upright  in  the  bottle. 

We  can  also  carry  out  the  experiment  with  burning  sulphur  held  in 
a  long-handled  spoon  (combustion  spoon).  The  handle  is  put  through 
the  cork.  After  burning  for  a  little  while,  the  sulphur  flame  "  goes 
out  "  and  the  bottle  has  in  it  a  gas  with  a  sharp  odor.  If  we  now  put 
into  the  bottle  a  burning  splinter,  or  a  candle,  it  will  not  continue  to 
burn. 

25.  How  Much  of  the  Air  Supports  Burning  ?-- The 
experiments  we  have  already  performed  show  us  that  a 
burning  body  needs  air.  Let  us  now  try  to  find  out 
whether  all,  or  only  a  part,  of  the 
air  takes  part  in  the  burning. 

We  can  use  a  short  candle,  such  as 
a  "  birthday"  candle  (Fig.  18). 
Soften  the  bottom  of  the  candle  by 
warming  it  and  then  press  it  against 
a  piece  of  tin,  such  as  a  jelly-glass 
cover,  until  it  sticks.  Now  set  the 
candle  upright  in  a  basin  containing 
water  to  the  depth  of  about  one 
inch,  and  light  the  candle.  When  it  is  burning  briskly, 
put  over  it,  and  into  the  water,  a  bottle  of  fresh  air.  At 
first  the  candle  flame  burns  just  as  it  does  in  the  outer 
air,  but  soon  it  dies  down  and  goes  out.  When  the  flame 
goes  out  and  the  gas  left  in  the  jar  becomes  cool,  water 
rises  into  the  bottle.  What  does  this  mean?  It  means 
that  there  is  less  air  in  the  jar  after  the  candle  has  burned 
than  there  was  before.  The  water  rises  to  take  the  place 
of  that  part  of  the  air  which  has  been  used  up. 


FIG.  18.  —  As  the 
candle  burns,  it  uses  up 
part  of  the  air  of  the 
bottle. 


FIRE 


Another  material  that  helps  us  in  our  study  of  burning  is  phos- 
phorus, but  the  experiment  must  be  performed  by  the  teacher,  since 
phosphorus  burns  with  great  fierceness.  There  are  two  kinds  of. 
phosphorus :  one  is  a  red  powder  and  the  other  a  yellow,  waxy  solid 
that  comes  in  sticks  which  look  like  lemon  stick  candy.  The  red  is 
much  safer  to  handle  and  to  keep.  If  the  yellow  is  used,  it  must  be 
kept  under  water  and  cut  under  water,  or  it  may  take  fire  of  itself 
and  cause  serious  burns.  For  this  reason,  the  piece  cut  off  for  use  must 
be  handled  with  forceps  or  tongs,  never  with  the  fingers.  You  would 
never  guess  that  such  an  active  substance 
could  be  a  part  of  our  bones  and  of  the 
rock  phosphate  that  is  put  upon  soil, 
but  it  is  so. 

Let  the  teacher  set  up  the  apparatus  of 
Fig.  19.  The  vessels  needed  are  a  pint 
fruit  jar  and  a  shallow  pan  containing 
water.  The  phosphorus  is  put  on  a 
holder  that  reaches  about  halfway  up  the 
jar.  The  holder  may  be  a  strip  of  "  tin  " 
with  a  horizontal  top  about  the  size  of  a 
25-cent  piece,  or  it  may  be  a  small 
covered  with  a  disk  of  "tin. 


FIG.  19.  —  The  phosphorus 
burns  until  it  has  used  up  that 
part  of  the  air  which  permits 
burning  to  go  on. 


cork  fastened  to  a  wire  and 
The  lower  end  of  the  strip  or  wire  is 
put  through  a  hole  or  a  narrow  slit  in  a  piece  of  sheet  lead  or  into  a 
rubber  stopper,  so  that  the  phosphorus  holder  will  stand  upright. 
A  floating  support  for  the  phosphorus  is  often  used ;  it  may  be  made 
out  of  a  thin,  flat  cork  with  a  disk  of  tin  laid  upon  it  to  protect  it. 
When  the  support  is  ready,  we  set  the  phosphorus  on  fire,  put  the  jar 
of  air  over  it,  and  press  the  jar  against  the  bottom  of  the  pan. 

The  phosphorus  will  burn  for  a  time,  forming  a  dense,  white  smoke ; 
then,  although  there  is  still  some  phosphorus  left,  it  stops  burning. 
Finally  the  smoke  dissolves  in  the  water,  leaving  the  gas  in  the  jar 
quite  clear  and  transparent,  like  the  air  itself.  But  long  before  the 
smoke  disappears,  water  will  rise  into  the  jar. 

Let  us  examine  the  bottle  in  which  the  candle  has 
burned,  or  the  jar  in  which  phosphorus  has  burned. 


32  JUNIOR  SCIENCE 

What  fraction  of  its  volume  is  filled  with  water?  Is  it 
I,  J,  i>  or  what?  To  find  out,  we  can  close  the  mouth  of 
the  bottle  or  jar,  under  water,  with  a  card  and  then 
remove  the  jar  from  the  water  and  set  it  upright  on  the 
table.  If  we  put  a  burning  splinter  or  candle  into  the  jar, 
we  find  that  the  gas  in  the  jar  is  inactive  and  does  not 
allow  burning  to  go  on. 

26.  Is  Air  a  Mixture  ?  —  By  burning  a  candle  or  some 
phosphorus  in  a  jar  of  air  we  find  out  a  very  wonderful 
thing.     When  the  experiment  is  carried  out  with  great 
care,  the  water  rises  into  the  jar  until  it  fills  about  \  of  it 
(nearly  21  per  cent).     Many  other  burning  substances 
act  upon  air  in  this  way ;  that  is,  after  they  have  used 
up  about  \  of  the  air,  they  do  not  act  further.     How  can 
we  explain  this  fact?     The  explanation  is  that  the  air 
consists  of  at  least  two  different  gases  :  one  that  permits 
burning  to  go  on  and  another  that  does  not.     The  active 
gas,  which  unites  with  substances  when  they  burn,  is 
called  oxygen.     The  inactive  gas,  making  up  about  f  of 
the  air,  is  nitrogen  (mixed  with  small  amounts  of  some 
other  gases).     The  air  is  oxygen  diluted  with  nitrogen, 
much  as  lemonade  is  lemon  juice  diluted  with  water, 

27.  How  Can  We  Explain  Burning?  —  We  can  now 
understand  what  the  strange  phenomenon  called  burn- 
ing, or  fire,  really  is.     Burning  is  the  uniting  of  a  body 
with  the  oxygen  of  the  air.     The  burning  body  and  the 
oxygen  rush  together  so  vigorously  that  heat  and  light 
are  produced.     The  burning  body  sometimes  disappears, 
as  far  as  we  can  tell  by  our  senses,  but  if  we  have  the 
skill  and  the  patience,  we  can  prove  that  it  has  merely 


FIRE  33 

united  with  oxygen,  and  we  can  collect  the  invisible 
materials  that  are  formed.  The  white  smoke  formed 
when  phosphorus  burns  contains  both  the  phosphorus  that 
was  used  up  in  burning  and  the  oxygen  that  united  with  it. 

Another  name  for  burning  is  combustion.  A  substance 
like  wood,  coal,  or  fuel  gas,  which  burns  in  the  air  is  a 
"  combustible  substance/'  or,  simply,  a  combustible. 

28.  What  is  a  Flame  ?  —  Have  you  ever  asked  your- 
self, as  you  watched  the  flame  of  a  bonfire  leap  high  into 
the  air,  what  a  flame  really  is,  and  how  it  can  reach  out 
so  far  from  the  burning  body?  And  have  you  noticed 
that  a  jet  of  gas,  or  a  candle,  or  a  piece  of  wood  burns 
with  a  flame,  while  a  piece  of  burning  charcoal  or  coke 
merely  glows  ?  Why  is  this  ? 

To  find  out  the  reason,  let  us  study  the  quiet,  little 
flame  of  a  lighted  candle.  A  candle  consists  of  wax,  or 
tallow,  and  a  wick.  When  the  wick  is  set  on  fire,  some  of 
the  wax  is  melted,  and  the  liquid  wax  rises  through  the 
wick  into  the  flame,  where  it  is  burned.  In  a  kerosene 
or  alcohol  lamp  the  liquid  rises  through  the  wick  in  the 
same  way. 

If  we  look  at  the  flame  carefully,  we  see  that  it  consists 
of  a  dark,  central  part  surrounding  the  wick,  and  a  burn- 
ing, outer  part  that  gives  the  light.  How  can  we  find  out 
what  is  taking  place  in  the  central  part?  One  way  is 
to  hold  one  end  of  a  small  tube  in  it,  as  shown  in  Fig.  20. 
If  we  then  bring  a  burning  match  near  the  upper  end  of 
the  tube,  we  can  get  a  flame  there,  too.  What  does  this 
mean?  It  means  that  an  invisible,  combustible  gas  is 
formed  in  the  dark,  central  part  of  the  flame  and  passes 


34 


JUNIOR  SCIENCE 


up  through  the  tube.  On  the  wick  and  in  the  central 
part  of  the  flame  the  wax  is  being  turned  into  this  gas. 
Why  does  not  the  gas  burn  on  the  inside  of  the  flame? 
Because  the  air  gets  at  the  gas  only  on  the  outside.  So 
the  candle  flame  really  consists  of  a  burning,  outer  region 

surrounding   a    central   region   of   unburned 

gas ;  a  flame  is  a  burning  gas. 

We  can  show  in  other  ways  that  flames  are  burning 
gases.  Suppose  we  "  blow  out  "  a  candle  flame,  and  at 
once  hold  a  burning  match  just  above  the  wick.  By 
making  several  trials  we  shall  find  that,  even  with  the 
match  quite  a  distance  above  the  wick,  we  can  still 
relight  the  candle.  What  is  it  that  passes  from  the 
wick  into  the  air  and  is  set  on  fire  by  the  match?  The 
invisible  gas  formed  out  of  the  wax.  If  we  give  the  wick 
time  to  cool,  it  can  no  longer  turn  the  wax  into  a  gas ; 
then  we  cannot  relight  the  candle  without  heating  the 
wick  up  to  its  kindling  temperature.  We  can  carry  out 
the  same  experiment  with  a  kerosene  lamp. 


FIG.  20.  — 
In  the  center 
of  a  candle 
flame  there  is 
a  combustible 
gas  that  can 
be  drawn  off 
through  the 
glass  tube  and 
burned. 


If  we  watch  a  burning  piece  of  wood,  es- 
pecially a  burning  log,  we  see  that  gas  comes 
out  of  the  wood  in  little  jets  that  burn  with  flames  ;  often 
these  can  be  lighted  at  some  distance  from  the  wood. 
Soft  coal  gives  off  a  gas  in  the  same  way,  and  so  burns 
with  a  flame.  Coke  and  charcoal  burn  without  flames  be- 
cause they  have  no  combustible  gases  to  give  off  (cf.  §  36). 

29.  Exercises. —  1.  Why  are  paper  and  wood  used  in  kindling  a 
coal  fire? 

2.  How  can  a  "  burning  glass  "  start  a  fire?  Do  you  think  that 
broken  bottles  left  in  the  woods  might  act  as  burning  glasses  and  cause 
forest  fires? 


FIRE  35 

3.  Do  you  think  that  the  air  which  passes  out  through  the  stove- 
pipe when  there  is  a  fire  in  the  stove  contains  more,  or  less,  oxygen  than 
when  it  entered  the  front  of  the  stove?     Why? 

4.  If  we  wish  to  put  out  a  fire,  what  must  we  keep  away  from  it? 
How  can  this  be  done? 

5.  Is  water  a  combustible?      Is  it  a  supporter  of  combustion? 
When  water  is  turned  into  steam,  does  the   steam  burn  or  support 
combustion?  Try  this  by  putting  a  burning  match   into  the   steam 
that  comes  from  a  teakettle  in  which  water  is  boiling  hard.     Tell  how 
these  facts  explain  why  water  puts  out  a  fire. 

6.  Why  does  a  blanket  or  rug  put  out  a  fire? 

7.  If  your  clothes  are  set  on  fire,  ought  you  to  run  outdoors  to  get 
help?     Why?     What  ought  you  to  do? 

8.  Does  an  old  iron  stove  ever  show  any  signs  of  being  partly 
burned  up? 


CHAPTER  V 


OXYGEN,  THE  FIRE  GAS 

30.  How  Can  We  Prepare  Oxygen?  —  You  would 
naturally  think  that  the  easiest  way  to  get  oxygen  un- 
mixed with  nitrogen  would  be  to  remove  the  nitrogen  of 
the  air.  But  we  must  remember  that  the  oxygen  is  the 
active  gas,  and  that  burning  substances,  like  a  candle  or 

phosphorus,  always 
combine  with  the  oxy- 
gen and  leave  the 
nitrogen.  So  to  get 
oxygen  we  must  use 
chemicals  that  consist 
partly  of  oxygen  and 
we  must  get  the  oxy- 
gen out  of  these.  The 
most  common  way  to 
get  oxygen  is  to  heat 
a  mixture  of  two  substances  called  potassium  chlorate 
and  manganese  dioxide.  The  potassium  chlorate  is  a 
white  solid  ;  the  manganese  dioxide  is  a  black  one. 

The  apparatus  used  is  shown  in  Fig.  21 .  To  fill  three  or  four  8-ounce 
(250  cc.)  bottles  with  the  gas  we  use  about  J  of  a  test  tube  of  potassium 
chlorate  and  about  |  of  a  test  tube  of  manganese  dioxide.  Each  should 
be  in  the  form  of  a  fine  powder  and  the  two  should  be  mixed  carefully 
on  a  clean,  smooth  sheet  of  paper.  By  means  of  a  one-hole  stopper 

36 


FIG.  21. —  When  a  mixture  of  powdered 
potassium  chlorate  and  manganese  dioxide  is 
heated,  oxygen  is  given  off. 


OXYGEN,    THE   FIRE   GAS 


37 


we  connect  the  test  tube  containing  the  mixture  with  a  "  delivery  tube  " 
that  carries  the  gas  to  the  water  pan. 

To  heat  the  mixture  we  use  a  very  small,  smoky  flame  (a  candle 
flame  will  do) ;  bubbles  of  oxygen  will  soon  escape  from  the  end  of  the 
delivery  tube.  If  a  bottle  full  of  water  is  placed,  mouth  downward, 
over  the  end  of  the  delivery  tube,  the  oxygen  rises  into  the  bottle  and 
pushes  out  the  water.  We  thus  collect  the  gas  "  over  water,"  as  we 
collected  air  in  §  9,  Fig.  4. 

When  a  bottle  is  full  of  oxygen,  we  slip  under  it  a  piece  of 
cardboard,  or  of  sheet  glass,  and  then  set  it,  right  side  upward, 
on  the  table.  We  can  then  fill  other  bottles  with  the  gas.  If 
the  gas  is  to  be  kept  for  a  day  or  two,  the  bottle 
should  be  stoppered  tightly.  Pint  fruit  jars  with  rubber 
rings  and  tight  covers  make  excellent  storage  vessels 
for  gases. 

When  we  have  collected  enough  oxygen,  or  when 
all  has  come  off  that  will,  we  remove  the  delivery  tube 
from  the  water ;  then,  and  not  until  then,  should  we 
take  away  the  flame.  The  reason  for  this  care  is  that 
as  the  gas  in  the  test  tube  cools,  it  contracts  (cf .  §  12) ; 
if  cold  water  from  the  water  pan  is  forced  into  the 
hot  tube,  the  tube  may  break. 

We  shall  want  to  use  the  bottles  of  oxygen  in  the 
next  section  and  in  Chapter  VI. 


FIG.  22.  — 
When  hydrogen 
peroxide  solu- 
tion is  added 
to  manganese 
dioxide,  oxygen 
is  given  off. 


Another  way  of  getting  oxygen  is  shown  in  Fig.  22. 
For  this  we  need  only  a  glass  bottle  and  a  loose  cover, 
such  as  a  piece  of  sheet  glass.  Into  the  bottle  we  put 
manganese  dioxide  (or,  better,  potassium  permanganate) 
and  enough  water  to  just  cover  the  solid;  then  we  add 
some  hydrogen  peroxide  solution.  No  heating  is  needed. 
The  mixture  bubbles,  or  foams,  as  the  oxygen  rises 
through  the  water.  The  oxygen  pushes  the  air  out  of 
the  bottle  ;  soon  we  have  the  bottle  full  of  oxygen. 


38 


JUNIOR  SCIENCE 


31.  What  is  Oxygen  Like? — We  are  now  ready  to 
learn  some  of  the  properties,  or  qualities,  of  this  interest- 
ing gas.  We  can  see,  by  looking  at  the  bottles  of  oxygen, 
especially  after  they  have  stood  for  a  few  minutes,  that 
oxygen  has  no  more  color  than  air  has.  Perfectly 
pure  oxygen  has  neither  odor  nor  taste. 

If  we  light  a  pine  splinter,  and  put  it  for  an  instant 
into  a  jar  of  oxygen,  the  wood  burns  much  more  vigor- 
ously than   in   air.     If  we 
blow   out   the    flame,    and 
put    the    glowing    splinter 

*  into   the   bottle,    the    glow 

becomes  very  intense  and  the 
splinter  bursts  into  a  flame. 
In  this  way  we  can  tell  a 
bottle  of  oxygen  from  one 
of  air. 

A  burning  candle  burns 
more  vigorously  when  put 
into  oxygen.  Try  it,  if 
possible.  To  burn  sulphur  in  oxygen,  we  hold  it  in  a 
combustion  spoon  (cf.  §24).  We  light  the  sulphur  by 
holding  the  bowl  of  the  spoon  in  a  flame,  and  then  put 
the  spoon  into  a  bottle  of  oxygen  (Fig.  23,  a).  In  the 
air,  sulphur  burns  with  a  pale,  almost  colorless  flame, 
but  in  oxygen  the  flame  is  a  brilliant,  purple  one. 
By  smelling  cautiously  of  the  gas  formed  in  the  bottle 
we  learn  that  it  has  the  same  sharp  odor  as  the  gas 
formed  when  sulphur  burns  in  air.  We  call  it  sulphur 
dioxide. 


FIG.  23. —  a.  When  burning  sulphur 
is  put  into  oxygen,  it  burns  with  a 
brilliant,  purple  flame,  b.  Iron  wire 
burns  in  oxygen  with  a  brilliant  light 
and  a  shower  of  tiny  sparks. 


OXYGEN,    THE  FIRE  GAS  39 

We  do  not  see  iron  burn,  ordinarily,  in  air,  but  in  oxygen 
it  burns  (Fig.  23,  6)  with  a  brilliant  light  and  a  shower  of 
tiny  sparks.  The  best  way  to  show  the  burning  of  iron 
in  oxygen  is  to  use  a  piece  of  picture  cord  made  up  of 
fine  strands  of  iron  wire  and  to  put  on  one  end  of  the  cord 
a  tip  of  melted  sulphur  or  the  head  of  a  match ;  we  then 
light  the  sulphur,  or  match  head,  and  put  the  wire  at 
once  into  the  jar  of  oxygen.  The  shiny,  black  lump 
formed  on  the  end  of  the  wire  is  made  up  of  iron  and 
oxygen  ;  we  call  it  iron  oxide. 

32.  What  is  Oxidation?  —  Are  you  ready  now  to  learn 
the  meaning  of  some  important  words  ?     We  use  the  word 
"  oxidation  "  so  often  in  science  and  even  in  our  daily 
life,  that  we  should  get  some  idea  of  what  it  means.     We 
see  at  once  that  the  word  comes  from  "  oxide  "   (pro- 
nounced ox'id)  and  that  oxide  comes  from  "  oxygen." 
Oxidation    means    uniting    with    oxygen;  the    substance 
that  unites  with  oxygen  is  said  to  be  oxidized.     Thus 
the  iron  burning  in  oxygen  is  oxidized  to  iron  oxide. 
When  lead  is  heated  in  air,  it  is  oxidized  to  lead  oxide. 
The  white  smoke  formed  when  phosphorus  burns  in  air 
(cf.   §  25)   is  called  phosphorus  oxide.     When  coal  and 
charcoal,  which  consist  chiefly  of  carbon,  are  burned, 
the  oxide  formed  is  called  carbon  dioxide  (cf.  §37).     In 
this,  as  in  sulphur  dioxide,  the  syllable  "  di,"  meaning 
two,  is  put  before  "  oxide." 

33.  'Why  Does  Paint  Harden?  —  What  has  paint  to 
do  with  oxidation  ?    'Perform  the  following  experiment : 

Wet  the  inside  of  a  test  tube  with  linseed  oil  and  then  let  most  of 
the  oil  drain  out  of  the  tube.     Now  set  the  test  tube  upside  down  in 


40  JUNIOR  SCIENCE 

a  dish  of  linseed  oil  (Fig.  24)  and  leave  it  for  a  day  or  two.  The  oil 
will  rise  part  way  up  the  tube  and  then  stop ;  why  ?  What  substance 
does  linseed  oil  take  out  of  the  air? 

Common  paint  consists  of  linseed   (flaxseed)   oil  and 
turpentine,  mixed  with  "  white  lead  "  or  "  zinc  white  " 
and  perhaps  a  colored  substance.     White  lead  and  zinc 
white  are  used  to  give  the  paint  "  body/7  or  "  covering 
power/'     The  turpentine  not  only  thins 
the  paint,  but  assists  in  drying  the  oil. 

When  paint  dries,  its  linseed  oil  is 
oxidized  by  the  air  to  a  hard  gum  which 
does  not  dissolve  in  water  and  so  resists 
the  "washing"  of  the  rain;  this  gum 
forms  a  durable  coating  for  the  outside  of 
a  house  as  well  as  for  inside  woodwork. 

FIG.   24.  —  Lin- 
seed oil  unites  with  Considerable  heat  is  given  off  as  paint  dries ; 
the  oxygen  of  the  hence  heapg  of  painters'  cloths  sometimes  take  fire 
airm  the  test  tube.  . 
What  gas  remains?  without  our  knowing  why.     The   phenomenon  is 

called  spontaneous  combustion,  o  spontaneous  igni- 
tion, because  it  seems  to  take  place  "  of  itself."  But  it  is  a  case  of 
oxidation  as  truly  as  the  burning  of  a  match.  Cloths  containing 
linseed  oil  or  paint  should  never  be  left  about  a  building  except  in 
covered  metal  boxes  or  cans. 

34.  What  are  Rusting  and  Decay  ?  —  Do  you  sup- 
pose that  rusting  has  anything  to  do  with  oxidation? 
Carry  out  this  experiment : 

Wet  the  inside  of  a  test  tube  with  water  and  drain  off  mos{  of  the 
water.  Then  put  some  iron  filings  into  the  moist  tube  and  shake  them 
around  in  the  tube.  Pour  out  the  filings  that  do  not  stick  to  the  tube. 
Now  set  the  test  tube,  mouth  downward,  into  a  dish  of  water  and 
let  it  stand  for  a  day  or  two.  What  happens?  The  iron  rusts  and 


OXYGEN,    THE  FIRE  GAS  41 

at  the  same  time  water  rises  into  the  tube.     Finally  no  further  change 
takes  place.     What  does  the  iron  take  out  of  the  air  of  the  tube? 

Iron  rust  is  iron  oxide;  the  rusting  of  iron  is  really  the 
slow  oxidation  of  iron.  Heat  is  given  off,  as  in  the  burn- 
ing of  iron,  but  so  slowly  that  we  cannot  usually  notice 
it.  Many  other  metals  tarnish,  or  rust,  in  the  air. 

Decay.  —  What  becomes  of  the  dead  bodies  of  animals  and  plants 
and  of  dead  leaves,  wood,  and  fruit?  We  say  they  "  decay  "  or  "  rot." 
Decay  is  another  case  of  slow  oxidation.  Some  kinds  of  the  tiny 
plants  we  call  bacteria  (cf .  §  204)  bring  about  the  decay ;  they  use  up 
oxygen  in  doing  so. 

Have  you  ever  seen  a  "  hotbed,"  in  which  vegetables  may  be  grown 
during  the  winter  or  in  early  spring?  The  hotbed  is  a  large,  shallow 
box  with  a  glass  cover;  the  lower  part  of  the  box  is  surrounded  by 
manure.  The  heat  given  off  by  the  decay  of  the  manure  keeps  the 
ground  and  air  inside  the  box  warm,  so  that  vegetables  can  be  grown 
there  even  in  freezing  weather. 

Thus  we  see  that  oxygen  is  not  only  the  supporter  of  combustion, 
but  the  world's  great  purifier.  It  turns  the  remains  of  former  life 
into  harmless  substances,  so  that  the  life  of  the  present  time  may 
have  a  better  opportunity. 

35.  Exercises.  —  1.  What  names  should  you  give  to  the  substances 
formed  when  tin  and  zinc  burn  in  the  air? 

2.  What  substance  is  used  to  polish  stoves?     Why? 

3.  What  metals  are  used  to  cover  iron  to  keep  it  from  rusting? 
What  is  "  galvanized  "  iron? 

4.  Why  is  the  soil  in  some  places  red? 

5.  Of  what  are  "  tin  "  dishes  made?     Test  one  with  a  magnet. 

6.  Examine  an  old  washboard;  what  is  the  color  of  zinc  rust? 
Why  is  zinc  used  for  washboards  instead  of  iron  or  copper? 

7.  Covering  wood  with  an  oxide  protects  it  against  fire.     Why? 

8.  Let  an  empty  "  tin  "  can  rust  without  losing  any  material.     Does 
the  rusted  can  weigh  less,  or  more,  than  the  original  can?    Why? 


CHAPTER  VI 


CARBON  AND   CARBON  DIOXIDE 

36.  Why  Do   Some   Substances   Char?  —  Have  you 
thought,  as  we  studied  about  fire  and  oxidation,  how 
strange  it  is  that  the  active,  colorless  gas  oxygen  is  hidden 
away  in  the  red  iron  rust  and  the  white  potassium  chlorate, 
and    is    hidden    so    successfully    that    we 
would  never  guess   that  it  is   there,  until 
we  study  science?     Well,  the  oxygen  is  no 
more  skillfully  hidden  than  is  carbon,  the 
black  solid  that  we  see  in  coal  and  in  the 
"  black  lead,"  or  graphite,  of  our  pencils. 
Is  it   easy   for  you   to    believe   that   the 
FIG.  25.— The    brilliant   diamond,   the  hardest  substance 

baking-powder  / 

box  has  a  hole  in  known  to  man,  is  made  up  of  the  same 
black  carbon  that  is  present  in  coal ?  Yet 
fafe  [s  true ;  the  diamond  is  nearly  pure 
carbon. 

But  there  are  more  common  hiding 
places  for  carbon  than  in  diamonds.  Light 
a  match  or  splinter,  and  after  a  few  seconds  blow  it 
out  and  examine  the  partly  burned  end.  The  end  is 
now  a  black  substance,  no  longer  wood;  we  call  it 
charcoal.  Charcoal  is  a  form  of  carbon.  If  we  heat 
wood  in  a  deep  dish,  such  as  a  test  tube  or  a  baking- 
powder  box  (Fig.  25),  and  apply  a  burning  match  to 

42 


a  combustible  gas 
escapes  through 
the  hole  ;  this  gas 
comes  from  the 
wood. 


CARBON  AND  CARBON   DIOXIDE 


43 


the  open  end  of  the  dish,  we  find  that  the  heated  wood  is 
giving  off  a  gas  that  can  be  set  on  fire.  When  the  heating 
is  over,  charcoal  remains.  When  soft  coal  is  heated  in 
the  same  way,  coke  remains. 

Nearly  all  plant  and  animal  substances  behave  like  wood:  when 
they  are  heated,  they  char,  or  "  turn  to  carbon."     This  is  a  short  way 
of    saying    that    heating 
breaks  up  the  delicate  sub- 
stances formed  by  animals 
and  plants;   that  a  large 
portion  of  these  substances 
escapes  as  a  gas,  but  that , 
a  part  remains  behind  as 
solid  carbon. 

Men  make  charcoal  on 
a  large  scale  (Fig.  26)  by 
piling  wood  in  heaps,  cov- 
ering the  heaps  with  sod, 


FIG.  26.  —  Charcoal  is  made  by  the  heating  of 
covered  heaps  of  wood. 


and  setting  the  wood   on 

fire.     Small   openings   are 

left  to  allow  a  little  air  to  enter  and  the  gases  to  escape.    The  part 

of  the  wood  that  burns  gives  off  the  heat  which  is  needed  to  drive  off 

the  gases  from  the  wood  that  is  near  it.     This  is  exactly  what 

happens  in  the  half -burned  match. 

If  a  ton  of  wood  were  "  turned  into  charcoal/ '  would 
the  charcoal  weigh  more  or  less  than  a  ton  ?     Why  ? 

37.  What  Is  Formed  When  Carbon  Burns  ?  —  We  are 
now  ready  to  see  how  carbon  burns  in  air  or  oxygen  and 
to  learn  what  substance  is  formed.  Fasten  a  piece  of 
charcoal  to  a  wire,  or  hold  it  in  a  combustion  spoon' 
(cf.  Fig.  23,  §  31)  and  heat  the  charcoal  until  it  glows. 
If  we  then  hold  it  in  a  bottle  of  oxygen,  the  charcoal 


44  JUNIOR  SCIENCE 

burns  with  a  brilliant  light,  much  more  fiercely  than  in 
air.  After  the  charcoal  glow  has  gone  out,  put  about  a 
tablespoonf  ul  of  clear  lime  water  into  the  bottle  and  shake 
the  limewater  and  gas  together.  A  strange  thing  hap- 
pens; the  limewater  becomes  white,  or  "milky."  The 
milky  appearance  is  caused  by  a  multitude  of  white  parti- 
cles which  are  formed  in  the  limewater.  If  we  let  the 
bottle  stand,  the  particles  settle  to  the  bottom  of  the 
liquid. 

This  interesting  change  took  place  because  the  lime- 
water  found  carbon  dioxide  gas  in  the  bottle  in  which 
carbon  had  been  burned,  and  united  with  this  gas  to  form 
the  white  particles.  Carbon  dioxide  is  formed  when  the 
carbon  burns  in  oxygen,  just  as  iron  oxide  is  formed  when 
iron  burns  in  oxygen  (cf.  §  31).  We  use  limewater  to 
test  for  carbon  dioxide ;  that  is,  limewater  helps  us  to 
know  if  a  gas  is  really  carbon  dioxide  or  something  else. 
For  the  same  reason  we  used  a  glowing  splinter  to  test 
for  oxygen. 

If  we  burn  wood  and  coal  in  a  bottle  of  oxygen  or  air, 
and  make  the  limewater  test,  we  find  that  carbon  dioxide 
is  formed  in  these  cases  also.  If  we  burn  a  candle  in 
air  or  in  oxygen,  the  same  thing  is  true.  Men  have  even 
burned  diamonds  in  oxygen  and  have  proved  that  they 
produce  carbon  dioxide. 

38.  How  Can  We  Make  Carbon  Dioxide  ?  —  We  have 
already  had  Kone  answer  to  this  question :  we  can  make 
carbon  dioxide  by  burning  carbon  in  oxygen.  But  if 
we  want  to  use  several  bottles  of  it,  we  can  get  the  gas 
more  easily  by  putting  some  marble  in  a  bottle  and 


CARBON    AND   CARBON    DIOXIDE 


45 


adding  to  it  some  dilute  hydrochloric  acid.  The  marble 
froths  as  the  acid  acts.  The  frothing  is  caused  by  the 
gas  rising  in  tiny  bubbles  through  the  liquid,  just  as 
we  have  white-caps  on  the  lakes  or  ocean  from  the  air 
rising  through  the  waves. 

The  apparatus  is  shown  in  Fig.  27,  b.  The  long,  upright  tube  with 
the  rounded  funnel  at  the  top  is  called  a  "  thistle-tube  "  or  "  safety- 
tube."  Through  it  we  pour  the  acid  upon  the  marble.  We  collect 
the  gas  over  water  (cf.  §  30). 


FIG.  27.  —  a.    Carbon   dioxide  pushes   the   air  out  of  the    collecting    bottle. 
b.  Carbon  dioxide  may  be  collected  over  water,  as  oxygen  was. 

Instead  of  letting  the  gas  collect  over  water,  we  can  let  it  fall  into 
the  bottom  of  a  bottle ;  it  pushes  the  air  upward  and  out  of  the  bottle 
(Fig.  27,  a). 

In  place  of  marble  we  can  use  baking  soda  or  washing  soda,  and  in 
place  of  the  hydrochloric  acid  we  can  use  vinegar  or  lemon  juice.  We 
do  not  need  the  stopper,  thistle-tube,  and  delivery  tube  at  all ;  but  we 
can  use  a  bottle  with  a  glass  cover  (Fig.  22,  §  30).  If  we  put  marble 
(or  soda)  into  the  bottle,  and  add  the  acid,  the  carbon  dioxide  that  is 
formed  pushes  all  the  air  out  of  the  bottle. 

39.  What  is  Carbon  Dioxide  Like?  —  Carbon  dioxide 
is  colorless,  like  air  and  oxygen.  But  when  we  put  into 


46 


JUNIOR  SCIENCE 


the  gas  a  burning  match,  it  acts  differently  from  air  and 
oxygen.  The  burning  match  is  put  out  instantly.  If  we 
put  some  limewater  into  a  bottle 
of  carbon  dioxide,  the  limewater 
becomes  milky.  If  we  let  the  gas 
bubble  through  limewater,  the  same 
change  takes  place. 

We  can  perform  a  number  of  very  in- 
teresting experiments  with  carbon  dioxide ; 
here  is  one  of  them.  Into  the  bottom  of 
a  drinking  glass  or  a  fruit  jar  put  a  short 
piece  of  candle  and  light  it  (Fig.  28). 
Then  hold  over  the  glass,  or  jar,  a  bottle 
of  carbon  dioxide  and  pour  the  invisible 

gas,  just   as  if   you  were  pouring  water.     The   gas   falls   upon  the 

candle    flame   and   puts   it   out.     If  you  can  pour  carbon  dioxide 

downward,    is    it    heavier,    or    lighter, 

than  air? 

Another  way  to  learn  whether  carbon 

dioxide  is  a  light  gas  or  a  heavy  one,  is 

shown  in  Fig.  29.     If  we  balance  an  empty   / 

tin  can  or  paper  bag  upon  the  scales  and 

then  pour  carbon  dioxide  into  it,  the  can 

(or  bag)  sinks ;  this  proves  that  the  car- 
bon dioxide  is  heavier  than  air.    If  we  turn 

the  vessel  upside  down,  the  gas  falls  out, 

and  the  scales  become  balanced  once  more. 


FIG.   28.  —  Carbon  dioxide 
can  be  poured  like  water. 


FIG.    29.  —  A    vessel    filled 

40.     Why      DOCS      Soda      Water    with    carbon     dioxide    weighs 

more  than  when  full  of  air. 

Foam,  or  Effervesce?  —  Suppose 

we  make  an  imitation  of  soda  water.  Let  us  put  into 
a  pop-bottle,  or  some  other  kind  of  bottle  that  we 
can  stopper  tightly,  a  tablespoonful  of  baking  soda, 


CARBON  AND  CARBON  DIOXIDE  47 

enough  water  to  half  fill  the  bottle,  and  three  or  four 
teaspoons  of  lemon  juice,  or  vinegar,  or  dilute  hydro- 
chloric acid.  We  must  stopper  the  bottle  at  once  after 
adding  the  acid. 

At  first  the  liquid  froths,  or  effervesces,  as  the  carbon 
dioxide  bubbles  through  it.  But  in  a  short  time  the 
frothing  stops  almost  entirely.  The  carbon  dioxide  cannot 
escape,  and  is  therefore  compressed ;  in  this  compressed 
state  it  dissolves  more  easily  in  the  liquid.  But  when 
we  open  the  bottle,  especially  when  we  pour  the  liquid 
out  into  a  glass,  we  notice  a  strong  frothing.  As  the 
pressure  on  the  carbon  dioxide  is  now  released,  the  gas 
can  escape  from  the  liquid. 

Beneath  the  surface  of  the  ground  there  are  both  water  and  carbon 
dioxide.  They  are  under  greater  pressure  than  at  the  surface,  because 
of  the  rock  above  them.  For  this  reason  more  carbon  dioxide  can 
dissolve  in  underground  water  than  in  water  at  the  surface.  When 
water  charged  with  a  great  deal  of  carbon  dioxide  reaches  the  surface, 
as  in  some  springs,  it  effervesces  like  soda  water.  We  call  such  springs 
"  carbonated  "  springs. 

41.   How   Does   Carbon  Dioxide   Put   Out  Fires?  — 

When  you  saw  that  carbon  dioxide  could  be  poured  upon 
a  burning  candle,  did  the  idea  come  to  you  that  we  mighfr 
use  this  gas  to  put  out  a  fire?  Men  had  this  idea  years 
ago  and  have  used  it  in  fire  extinguishers.  In  the  ordi- 
nary "  chemical  "  fire  engine,  such  as  is  used  to  protect  a 
school  building  or  a  factory  (Fig.  30),  the  carbon  dioxide 
is  formed  from  the  action  of  baking  soda  with  an  acid. 
The  baking  soda  is  dissolved  in  water  and  the  solution 
is  kept  in  a  metal  tank.  A  bottle  of  sulphuric  acid  is 


48 


JUNIOR  SCIENCE 


fastened  in  the  upper  part  of  the  tank.  When  we  turn 
the  tank  upside  down,  the  acid  is  spilled  out  of  the  bottle 
and  acts  with  the  soda,  forming  carbon  dioxide.  The 
pressure  of  the  carbon  dioxide  forces  out  some  of  the 
water  and  carbon  dioxide ;  these  two  put  out  the  fire. 

A  mixture  of  baking  soda  and  dry  sawdust  is  also 
used  to  put  out  fires,  especially  gasoline  fires.  The 
burning  substance  heats  the  soda  and  it 
gives  off  a  large  amount  of  carbon  dioxide. 
The  invisible  carbon  dioxide  covers  the 
burning  body  like  a  blanket  and  keeps  the 
oxygen  away  ;  hence  burning  cannot  go  on. 
42.  How  Does  Carbon  Dioxide  Get 
into  the  Air?  —  Do  you  need  any  proof 
that  there  is  carbon  dioxide  in  the  air? 
Then  set  a  shallow  dish  of  limewater  in  the 
air  in  your  schoolroom  and  watch  it  for  an 
hour  or  two.  It  will  become  covered 
with  a  white  crust,  or  scum,  which  con- 
sists of  the  solid  that  makes  limewater 
milky.  The  chemist  calls  this  calcium  carbonate  ;  lime- 
stone and  marble  are  natural  forms  of  it. 

How  does  carbon  dioxide  get  into  the  air?  We  have 
learned  that  when  charcoal  burns  in  oxygen,  carbon 
dioxide  is  formed.  When  wood,  coal,  paper,  a  candle, 
gasoline,  or  any  other  substance  that  contains  carbon,  is 
burned  in  air  or  in  oxygen,  carbon  dioxide  is  formed. 
So  we  see  that  an  enormous  amount  of  carbon  dioxide 
must  get  into  the  air  from  all  ordinary  burning. 

Carbon  dioxide  gets  into  the  air  not  only  from  burning, 


FIG.  30.  —  A 
fire  extinguisher. 
The  liquid  in  the 
tank  is  a  solution 
of  soda.  The 
bottle  at  the  top 
contains  sulphu- 
ric acid. 


CARBON  AND   CARBON   DIOXIDE 


49 


but  also  from  the  breathing,  or  respiration,  of  animals 
and  plants.  You  can  readily  prove  that  you  yourself 
breathe  out  a  great  deal  of  carbon  dioxide,  by  blowing 
your  breath  through  limewater  (Fig.  31).  The  lime- 
water  will  become  very  milky. 

A  third  way  in  which  carbon  dioxide  gets  into  the  air 
is  by  the  decay  of  such  things  as  wood,  leaves,  and  fruit, 
and  the  bodies  of  dead  animals  (cf.  §  34). 
The  carbon  of  the  decaying  substances  is 
changed  chiefly  to  carbon  dioxide,  which 
enters  the  air  just  as  if  the  substance  had 
been  burned. 

43.  How  Is  Carbon  Dioxide  Removed 
from  the  Air? — What  becomes  of  all 
the  carbon  dioxide  that  is  poured  into 
the  air?  It  is  given  off  by  every  living 
creature,  by  every  fire,  and  by  all  decay. 
Why  does  not  carbon  dioxide  become  so 
plentiful  that  fires  will  no  longer  burn 
and  that  animals  and  plants  will  not  be 
able  to  live?  Can  we  answer  this  ques- 
tion by  an  experiment?  The  experiment 
(Fig.  32)  is  to  let  green  plants,  in  the  presence  of  sunlight, 
act  upon  water  containing  carbon  dioxide. 

First  make  some  carbon  dioxide,  as  in  §  38,  from  marble  chips  and 
an  acid.  Half  fill  a  large,  small-mouthed  bottle  with  water  and  drive 
out  the  air  that  remains  by  passing  carbon  dioxide  into  the  bottle 
(the  bottle  to  be  mouth  upward) .  Then  stopper  the  bottle  and  shake 
the  water  and  carbon  dioxide  vigorously  together.  In  this  way  you 
can  make  a  great  deal  of  carbon  dioxide  dissolve  in  the  water. 


FIG.  31.  — 
Blow  your  breath 
through  lime- 
water  ;  the  lime- 
water  becomes 
"milky"  from 
the  carbon  di- 
oxide you  exhale. 


50 


JUNIOR  SCIENCE 


Into  a  deep  glass  jar  ("  battery  jar  ")  place,  upside  down,  a  large 
funnel  filled  with  spinach  or  parsley;  then  almost  fill  the  jar  with 
the  carbonated  water.  The  stem  of  the  funnel  must  be  entirely  under 
water.  Now  fill  a  test  tube  with  water,  close  its  mouth  with  your 
thumb,  set  the  test  tube  mouth  downward  into  the  battery  jar,  and 
slip  it  carefully  over  the  stem  of  the  funnel.  Then  set  the  whole 
apparatus  in  bright  sunlight  for  an  hour  or  two. 

If  you  watch  carefully,  you  will  find 
that  bubbles  of  gas  rise  into  the  test 
tube.  When  enough  gas  has  been  col- 
lected, remove  the  test  tube  carefully  from 
the  funnel,  close  the  tube,  under  water, 
with  your  thumb,  and  then  turn  the  tube 
right  side  up.  Now  find  out  what  the 
gas  is  by  putting  into  it  a  splinter  with 
a  glowing  tip.  The  gas  is  oxygen. 


Oxygen 


Water 


Carbonated 
"Water 


Leaves 
FIG.    32.  —  When 


Does   this   experiment  help  us 
green    to    answer    our    question    as    to 
how  carbon    dioxide   is   removed 
up  the  carbon  dioxide  and    f rom  the  air  ?     The  answer  is  that 

set  oxygen  free.  . 

green  plants  use  up  carbon  dioxide 

and  give  back  oxygen  to  the  air.  Thus,  in  spite  of  all 
the  ways  in  which  oxygen  is  used  up,  we  still  have  it  in 
the  air. 

How  is  the  carbon  dioxide  removed  in  winter?  Does 
all  the  earth  have  winter  at  the  same  time  ? 

44.  How  Do  Plants  Help  Animals  ?  —  In  thinking  of 
the  ways  in  which  plants  help  animals,  we  must  consider 
that  plants  are  not  only  the  food  of  animals,  but  that 
they  prepare  and  purify  the  air  for  the  use  of  the  animals, 
as  we  have  just  learned.  This  careful  balance  between 
the  action  of  plants,  which  remove  carbon  dioxide  from 


CARBON  AND   CARBON   DIOXIDE  51 

the  air  and  give  back  oxygen,  and  the  action  of  the  ani- 
mals, which  do  the  opposite,  is  one  of  the  most  interest- 
ing facts  man  has  discovered.  You  can  study  this  bal- 
ance in  an  aquarium.  If  you  have  some  small  animals, 
such  as  goldfish,  in  the  aquarium,  and  the  right  quantity 
of  water  plants,  the  water  will  not  grow  stale,  but  the 
plants  will  use  up  the  carbon  dioxide  given  off  by  the 
animals  and  will  return  the  oxygen  to  the  animals  for 
their  future  use. 

45.   Exercises.  —  1.   How  may  a  stove  make  the  air  of  a  room  unfit 
to  breathe  ?     Is  there  any  danger  in  sleeping  in  a  room  having  a  stove  ? 

2.  When  soda  is  put  with  tomatoes,  a  foaming  takes  place ;  why? 

3.  If  a  candle  is  lowered  into  an  old  well  and  goes  out,  what  gas 
may  be  in  the  well?     How  did  it  get  there?     Should  a  man  go  into 
such  a  well? 

4.  Is  there  any  soda  in  soda  water?     What  causes  its  frothing? 

5.  Name  six  white  substances  which  are  partly  made  up  of  carbon. 
Name  two  transparent  ones. 

6.  Coal  and  diamonds  are  each  largely  carbon;  why  the  great- 
difference  in  their  values  ? 

7.  If  you  have  a  bottle  of  oxygen  and  one  of  carbon  dioxide  and 
neither  bottle  has  a  label,  how  can  you  tell  which  is  which? 

8.  Would  a  carbon  dioxide  fire  extinguisher  work  better  with  a  fire 
near  the  floor  or  with  one  near  the  ceiling? 


CHAPTER  VII 
THE  AIR  WE  BREATHE 

46.  Why  Do  We  Breathe  ?  —  Have  you  ever  thought 
of  the  interesting  act  we  call  breathing  and  asked  your- 
self how  and  why  we  breathe  ?  Of  course  all  of  us  know 
what  breathing  is.  It  is  the  taking  of  outside  air  into 
the  lungs  and  then  expelling  the  used  air  from  the  .lungs. 
Is  air  changed  by  breathing?  To  answer  this  question, 
carry  out  the  following  experiment : 

Provide  a  bottle  with  a  cardboard  cover  and  make  a  hole  in  the 
cover.  Put  a  glass  tube  or  lemonade  "  straw  "  through  the  hole  and 
into  the  bottom  of  the  bottle.  Hold  your  breath  as  long  as  possible 
and  then  blow  it  through  the  tube  into  the  bottle.  Now  test  the 
air  in  the  bottle  with  a  burning  stick.  Does  the  stick  continue  to 
burn?  What  has  the  air  lost?  What  has  it  gained? 

Men  haye  found  that  while  the  air  which  rushes  into 
the  lungs  is  more  than  one-fifth  oxygen  and  contains 
very  little  carbon  dioxide,  the  air  which  leaves  the  lungs 
has  lost  a  part  of  its  oxygen  and  has  gained  carbon 
dioxide..  Thus  we  see  that  not  only  in  supporting  fire  is 
oxygen  used  and  carbon  dioxide  formed,  but  also  in  sup- 
porting life. 

Why  then  do  we  breathe  ?  The  answer  seems  to  be  to 
get  oxygen  into  the  body  and  to  remove  carbon  dioxide 
from  the  body.  We  must  remember,  too,  that  the  oxygen 

52 


THE   AIR   WE   BREATHE  53 

we  breathe  does  not  stop  in  the  lungs,  but  passes  through 
the  walls  of  the  lungs  into  the  blood  vessels ;  it  is  then 
carried  by  the  blood  to  all  parts  of  the  body.  The  whole 
process  by  which  oxygen  gets  to  the  cells  of  the  body  is 
called  respiration. 

A  grown  man  takes  into  his  lungs  about  350  cubic  feet 
of  air  in  a  day.  How  much  of  this  is  oxygen?  "  Why," 
you  will  ask,  "  do  we  need  to  take  in  so  much  oxygen?  " 
The  answer  is  that  we  need  oxygen  to  oxidize  the  food 
we  eat.  The  digested  food,  like  the  oxygen,  is  carried 
by  the  blood  to  all  parts  of  the  body.  The  oxidation  of 
our  food  is  a  change  somewhat  like  the  burning  of  coal 
in  a  stove ;  at  any  rate,  it  produces  heat,  and  carbon 
dioxide  is  formed,  just  as  when  a  candle  burns  in  a  bottle 
of  air  (cf.  §  24).  It  is  only  by  the  oxidation  of  our  food 
that  we  get  the  power  to  move  and  to  do  work.  The 
heat  produced  by  this  same  oxidation  keeps  our  bodies 
at  about  98.6°  Fahrenheit,  winter  and  summer,  as  long 
as  we  are  well. 

Water  animals  need  oxygen  to  oxidize  their  food  and  make  move- 
ment possible,  just  as  land  animals  do.  Such  creatures  as  fishes,  clams, 
and  tadpoles  depend  upon  the  oxygen  dissolved  in  the  water  in  which 
they  live.  Their  gills  act  in  place  of  our  lungs  in  taking  up  oxygen 
and  giving  off  carbon  dioxide. 

47.  Why  Do  We  Need  Ventilation?  —  Do  you  know 
what  ventilation  means?  It  comes  from  a  word  mean- 
ing "  wind/7  and  means  the  bringing  of  fresh  air  into  our 
houses  and  the  taking  out  of  the  used  air.  Do  you 
realize  how  bad  it  is  to  breathe  the  same  air  over  and  over 
again  ?  Doctors  know  that  people  who  have  good  health 


54  JUNIOR  SCIENCE 

in  warm  weather,  when  they  keep  their  doors  and  win- 
dows open,  have  colds  and  other  troubles  of  the  nose, 
throat,  and  lungs  almost  as  soon  as  cold  weather  comes 
and  their  houses  are  tightly  closed.  The  sealing  up  of 
the  openings  keeps  the  fresh  air  out  and  the  foul  air  in. 
This  is  especially  true  when  storm  windows  and  weather 
strips  are  used  to  "  keep  out  the  cold." 

It  has  been  calculated  that  in  one  hour  a  healthy  man  makes  about 
4000  cubic  feet  of  air  unfit  to  breathe.  This  means  that  if  one  man 
were  put  into  a  perfectly  tight  room  20  feet  square  and  10  feet  high, 
he  alone  would  make  the  air  bad  hi  one  hour.  Of  course  rooms  are 
not  air-tight  and  so  a  good  deal  of  fresh  air  gets  in  through  cracks 
around  doors  and  windows,  even  when  we  do  not  try  to  ventilate. 
Schoolrooms,  since  they  have  a  large  number  of  persons  in  a  small 
place,  need  special  care  to  make  them  safe.  According  to  a  Massa- 
chusetts law,  each  pupil  should  get  at  least  1800  cubic  feet  of  air  every 
hour.  If  a  person  coming  in  from  out  of  doors  notices  that  the  room 
has  an  odor,  the  air  has  been  breathed  too  often.  The  class  work  in 
such  a  room  is  probably  dull  and  slow. 

48.  Fresh  Air  and  Tuberculosis.  —  Most  of  us  prob- 
ably know  some  one  who  has,  or  has  had,  tuberculosis, 
or  "  consumption."  It  is  called  the  "  Great  White 
Plague/'  because  it  causes  the  death  of  so  many  people. 
Persons  suffering  from  this  disease  are  now  generally 
given  the  fresh-air  treatment.  They  live  in  tents  in 
the  open  air,  winter  and  summer,  day  and  night.  Of 
course  they  must  be  warmly  clothed  and  must  have  very 
nourishing  food.  Nearly  all  who  begin  the  fresh-air 
treatment  when  they  are  first  attacked  by  the  disease 
are  able  to  cure  themselves.  Many  healthy  persons  keep 
themselves  well  by  sleeping  out  of  doors  winter  and 


THE  AIR   WE  BREATHE  55 

summer.  This  "  sleeping-out  "  gives  the  lungs  every 
chance  for  fresh  air. 

49.  How  Do  We  Ventilate  Our  Houses?  —  Do  you 
want  to  know  how  our  houses  are  ventilated  naturally? 
Then  carry  out  this  simple  experiment : 

Open  the  door  leading  from  a  warm  room  into  a  cold 
one  and  hold  a  lighted  match  near  the  top  of  the  door- 
way. You  will  find  that  the  match  flame  is  blown  from 
the  warm  room  toward  the  cooler  one.  Now  hold  the 
match  near  the  bottom  of  the  doorway  ;  the  match  flame 
is  blown  from  the  colder  toward  the  warmer  room.  The 
flame  shows  us  how  the  invisible  air  currents  are  moving. 
Cold  air  flows  in  at  the  bottom  of  the  room  to  take  the 
place  of  the  warmer  air  which  rises  and  flows  out  at  the 
top.  The  reason  for  this  has  already  been  learned  (cf. 
§  12).  When  air  is  warmed  it  expands,  so  that  a  cubic 
foot  of  warm  air  will  weigh  less  than  a  cubic  foot  of  cold 
air.  You  have  probably  all  seen  the  hot-air  toy  balloons 
that  are  sent  up  in  the  evening  celebration  of  the  Fourth 
of  July.  A  wick  soaked  in  kerosene  is  fastened  at  the 
bottom  of  the  balloon,  which  is  open.  The  burning  wick 
heats  the  air  that  rises  into  the  balloon  and  the  balloon 
becomes  filled  with  warm  air.  As  the  balloon  full  of 
warm  air  is  lighter  than  if  filled  with  cool  air,  it  rises, 
just  as  a  cork  would,  if  you  were  to  let  go  of  it  under 
water. 

Natural  ventilation  is,  then,  the  method  of  ventilating 
which  depends  upon  the  entrance  of  cold  air  at  the 
bottom  of  a  room  and  the  leaving  of  warm  air  above. 
You  see  that  natural  ventilation  must  work  better  in 


56 


JUNIOR  SCIENCE 


winter  than  in  summer,  because  in  winter  there  is  such 
a  great  difference  between  the  temperatures  inside  and 
outside  the  house.  Weather  strips,  storm  doors,  and 
storm  windows  are  really  used  to  prevent  ventilation 
and  to  hold  the  warm  air  inside  the  house. 

50.  How  Can  We  Ventilate  Our  Bedrooms  ?  —  Not 
only  the  living-rooms  of  the  house,  but  also  the  bed- 
rooms, need  to  be  ventilated  with  great 
care.  Rooms  used  in  the  daytime  are 
sure  to  have  a  good  deal  of  fresh  air 
brought  into  them  by  the  opening  of 
doors  as  people  go  in  and  out.  But 
there  is  very  little  chance  for  a  closed 
bedroom  to  get  fresh  air.  So  we  should 
have  at  least  one  window  open  every 
night  and  the  room  should  be  thor- 
oughly aired  during  the  day. 


FIG.  33.  —  A  board 
with  boxed  holes  allows 
air  to  enter  and  leave 
a  room  even  in  stormy 
weather. 


Because  a  bedroom  is  kept  cold  does  not 
mean  that  the  air  is  pure ;  cold  air,  if  not 
changed  often,  may  be  just  as  foul  as  warm 
air.  It  is  a  good  plan,  if  the  weather  is  too 

stormy  to  allow  a  window  to  be  open  from  the  bottom,  to  lower  the 
upper  sash  part  way.  The  opening  at  the  top  and  the  space  between 
the  sashes  make  the  two  openings  needed  for  the  movement  of  air.  If 
a  board  with  boxed  holes  (Fig.  33)  is  put  under  the  lower  sash,  the 
air  will  enter  through  the  holes  and  pass  out  between  the  sashes. 

The  air  of  our  houses  becomes  unfit  to  breathe,  not  so  much  be- 
cause it  contains  impurities  as  because  it  is  not  in  motion. 

51.  How  to  Ventilate  the  Schoolroom.  —  If  a  school- 
room depends  upon  natural  ventilation,  how  shall  we  venti- 
late it  ?  Shall  we  have  several  windows  each  open  a  little, 


THE  AIR   WE   BREATHE 


57 


or  one  open  a  great  deal  ?  If  we  try  the  results,  we  shall 
find  that  one  window  opening  gives  stray  currents  of  air 
(drafts)  ;  while  several  small  openings  will  give  just  as  much 
circulation,  but  no  person  will  feel  a  draft.  The  openings 
should  be  on  the  side  of  the  building  opposite  the  wind. 

When  a  stove  is  used  to  heat  a  room,  air  currents  are 
made  by  the  stove.  As  the  air  near  the  stove  is  heated, 
it  rises  and  flows  away  along  the  ceiling ; 
at  the  same  time  the  cold  air  moves  along 
the  floor  toward  the  stove,  to  be  heated 
in  its  turn. 

If  a  stove  "  drum  "  is  used  (Fig.  34), 
it  protects  the  persons  near  the  fire  from 
too  great  heating  and  sets  up  stronger 
currents  than  the  stove  alone.  The  cold 
air  comes  from  the  farthest  corners  of  the 
room,  is  heated,  rises,  and  flows  back  to 
the  corner  from  which  it  came.  In  this 
way  the  room  is  heated  and  ventilated 
evenly. 


FIG.  34.  —  Such 
drums  as  these 
were  used  to  help 
heat  and  ventilate 
the  barracks  of  our 
training  camps. 


In  large  school  buildings  the  heating  and  ventilating  are  done 
together  by  what  is  called  forced  ventilation.  One  method  is  to  force 
fresh  air  over  steam  by  means  of  rotating  fans  in  the  basement.  After 
the  air  has  been  heated,  it  is  forced  into  the  schoolroom.  The  impure 
air  escapes  through  openings  in  the  walls  or  ceiling.  Sometimes  the 
impure  air  is  removed  from  the  room  by  means  of  rotating  fans  and 
warm  fresh  air  is  brought  in  through  small  holes  near  the  floor.  .Find 
out  how  your  school  building  is  ventilated. 

52.   Do  We  Need   Moisture   in   the  Air  ?  —  Do   you 

remember  days  when   the   air  was   "  sticky  "   and    the 


58  JUNIOR  SCIENCE 

perspiration  did  not  evaporate?  If  you  were  to  ask  a 
scientist  what  is  the  trouble  on  such  days,  he  would 
tell  you  that  there  is  too  much  moisture  in  the  air.  Then, 
on  other  days,  the  moisture  of  the  skin  evaporates  too 
rapidly  and  leaves  the  skin  parched  and  dry.  The  reason 
in  this  case  is  that  on  these  days  the  air  holds  too  little 
moisture  and  so  takes  it  up  from  everything  that  con- 
tains it,  including  our  skin  and  the  linings  of  the  nose, 
throat,  and  lungs.  When  our  houses  are  closed  up  in 
the  winter  and  heated  to  the  temperature  of  summer, 
the  amount  of  moisture  present  in  the  air  of  the  house  is 
almost  sure  to  be  too  small,  because  the  cold  air  which 
enters  has  its  power  of  taking  up  moisture  greatly  in- 
creased by  being  warmed.  Breathing  of  this  warm,  dry 
air  makes  it  very  easy  for  us  to  "  catch  cold/7  People 
who  have  studied  ventilation  say  that  the  amount  of 
moisture  in  a  room  should  be  so  great  that  some  of  it 
will  be  deposited  as  dew  and  frost  on  the  windows  in 
cold  weather.  Rooms  which  are  heated  by  steam  or 
hot  water  should  also  have  the  air  moistened  by  pans 
full  of  water  near  the  radiators.  Hot-air  furnaces  have 
pans  for  water  ;  these  should  be  kept  full. 

53.  How  Do  We  Breathe  ?  — People  often  think  that 
in  some  way  we  "  suck  "  air  into  the  lungs.  This  is  not 
true.  What  happens  is  that  as  we  allow  the  muscles  of 
the  chest  to  become  loose,  or  relaxed,  the  lung  cavity  be- 
comes larger.  The  pressure  of  the  air  in  the  lungs  is 
then  less  than  the  pressure  of  the  air  outside ;  so  the 
outer  air  rushes  into  the  lungs.  When  the  chest  muscles 
contract,  and  become  shorter,  they  make  the  lung  space 


THE   AIR   WE   BREATHE  59 

smaller.  Part  of  the  air  is  thus  forced  out  of  the  lungs. 
Our  regular  breathing  is  caused  by  the  regular  con- 
tracting and  relaxing  of  the  chest  muscles.  We  shall 
learn  more  about  breathing  in  Chapter  XXXVIII. 

54.  Proper  and  Improper  Breathing.  —  We  learned  in 
the  beginning  (cf.  §  5)  that  science  should  help  us  to  live 
healthy  lives.  One  way  in  which  it  does  this  is  in  ex- 
plaining the  importance  of  fresh  air  and  good  methods 
of  breathing.  The  air  goes  through  the  nose,  throat,  and 
windpipe  before  it  enters  the  lungs.  If  the  nose  is 
healthy,  the  air  is  filtered  from  dust  and  the  germs  which 
cling  to  the  dust.  It  is  also  warmed.  If  we  breathe 
through  the  mouth,  the  purifying  and  warming  effect 
of  the  nose  passages  is  lost  and  we  are  much  more  likely 
to  have  diseases  of  the  throat  and  lungs.  Mouth  breath- 
ing may  be  just  a  bad  habit ;  if  so,  we  should  overcome 
it  at  once.  It  may  be  caused  by  a  stoppage  of  the  nose 
by  colds  or  by  inflammation  of  the  nose  passages.  This 
should  be  cured.  But  mouth  breathing  may  also  be 
caused  by  growths  in  the  throat  ("  adenoids  "),  which 
partly  close  the  opening  from  the  nose  into  the  throat. 
These  should  be  removed  by  a  physician,  for  they  may 
cause  not  only  mouth  breathing  and  badly  formed  mouths, 
but  also  deafness.  Children  having  adenoids  often  seem 
to  be  stupid,  when  they  are  really  ill. 

We  should  all  practice  full  breathing,  with  head  and 
shoulders  erect,  so  that  all  parts  of  the  lungs  can  get 
fresh  air.  If  we  must  work  indoors  for  long  periods,  we 
should  go  out  of  doors  or  to  a  window  every  little  while, 
so  as  to  get  deep  breaths  of  fresh  air. 


60  JUNIOR  SCIENCE 

55.   Exercises. —  1.   Watch  a  person  who  breathes  through  his 
mouth ;  does  such  breathing  affect  his  appearance  ? 

2.  How  do  you  ventilate  your  sleeping-room?     How  should  it  be 
ventilated? 

3.  Tell  how  your  schoolroom  is  ventilated. 

4.  What  should  be  done  with  a  child  that  breathes  through  its 
mouth? 

5.  How  should  people  having  tuberculosis  be  treated? 

6.  What  is  the  real  value  of  breathing  exercises? 

7.  Is  there  any  evidence  of  a  greater  amount  of  moisture  in  the 
air  of  your  house  on  a  wash  day  than  on  other  days?     Tell  what 
happens  and  why. 


CHAPTER  VIII 
HEATING  THE  AIR  OF  THE  HOUSE 

56.  How  Do  We  Heat  the   House?  — What  do  we 

mean  when  we  say  that  we  "  heat  "  our  houses?  Is  it 
not  that  we  heat  the  air  of  our  houses  and  that  it  is 
through  the  heated  air  that  we  get  heat  to  the  objects  of 
the  house?  When  we  say  that  we  "  keep  in  the  heat" 
and  "  keep  out  the  cold/'  we  mean  that  we  keep  in,  or 
keep  out,  as  the  case  may  be,  the  heated  or  cold  air. 

57.  Fireplaces.  -  -  To  heat  their  dwellings  men  have 
used  open  fires,  fireplaces,  stoves,  hot-air  furnaces,  and 
hot-water,    steam,    and    electric    heaters.     The    Indian 
built  a  fire  on  the  floor  of  his  wigwam  and  let  the  smoke 
escape  through  a  hole  in   the  top.  •  The  Eskimo  uses 
blubber  (fat  obtained  from  the  whale)  as  the  fuel  to  heat 
his  house,  or  igloo.     You  may  imagine  the  smoke  and 
odors  of  these  barbarous  fires.     Civilized  man  has  im- 
proved greatly  on  these  methods. 

Nowadays  we  are  likely  to  think  of  the  fireplace  as 
merely  an  ornament,  but  it  is  really  very  useful,  no 
matter  how  the  house  is  heated.  It  helps  greatly  in 
ventilating  a  house  (cf.  §§  49  and  60),  for  it  carries  out 
the  air  near  the  floor  and  so  makes  room  for  fresh  air. 

In  the  early  days  of  this  country  all  heating,  both  for  cooking  and 
baking  and  for  heating  the  house,  was  done  by  the  fireplace  (Fig.  35). 

61 


62 


JUNIOR  SCIENCE 


The  andirons  kept  the  fuel  up  from  the  hearth,  so  that  air  currents 
would  be  drawn  through  the  fire.  A  crane  (a  swinging  frame)  could 
be  swung  out  over  the  fire.  From  it,  by  means  of  chains,  the  kettles 
were  hung.  .  Kettles  were  also  mounted  on  three  legs,  so  that  hot 
coals  could  be  put  under  them.  The  backlog  was  a  large  log  placed 
at  the  back  of  the  fireplace.  The  forestick  was  in  front,  on  the  and- 
irons; between  the  backlog  and  the  forestick  the  smaller  fuel  of  the 

fire  was  piled.  The 
backlog  sometimes 
lasted  several  days. 
Much  of  the  light  as 
well  as  the  heat  for 
the  household  came 
from  the  open  fire 
(cf.  §23). 

58.   Stoves. 

The  fireplace  is 
only  an  open  fire, 
such  as  a  bonfire, 
surrounded  with 
a  flue  for  the 
escape  of  the 
waste  gases.  The 
whole  fireplace 
opening  serves  for  the  entrance  of  fresh  air.  In  a  stove  the 
fire  is  surrounded  closely  on  all  sides.  There  are  dampers 
to  control  the  entrance  of  air  and  a  pipe  to  carry  off  the 
waste  gases.  In  place  of  the  andirons,  there  is  a  grate 
to  hold  the  fuel  up,  so  that  air  may  pass  through  it.  In 
a  cookstove  both  the  top  of  the  stove  and  the  oven  must 
be  heated,  hence  the  stove  has  a  "  back  damper  "  which 
does  not  allow  the  hot,  waste  gases  to  escape  at  once, 


FIG.  35.  —  Fireplaces  are  put  into  modern  houses 
both  for  beauty  and  for  use. 


HEATING   THE  AIR  OF   THE  HOUSE  63 

but  compels  them  first  to  travel  around  the  oven 
and  thus  to  heat  the  oven.  Examine  a  stove  and 
make  out  the  course  taken  by  the  air  that  passes 
through  it. 

59.  How  Does  a  Fire  Warm  Us  ?  —  Put  a  flatiron  on  a 
hot  stove;  what  happens?  The  iron  becomes  hot  be- 
cause the  heat  of  the  stove  is  passed  over,  or  conducted, 
directly  to  the  iron.  To  touch  the  handle  of  the  flat- 
iron  with  your  hand  would  make  a  painful  burn.  To 
prevent  this  you  use  a  nonconductor  of  heat,  such  as  a 
pad  of  cloth  or  asbestos,  or  a  wooden  handle.  If  you  put 
your  hand  into  warm  water,  the  heat  of  the  water  is 
conducted  to  your  hand.  When  you  put  your  hand  into 
cold  water,  your  hand  gives  heat  to  the  water.  The 
colder  body  or  object  is  warmed  by  conduction.  The 
air  that  touches  a  stove  is  also  warmed  by  conduction. 

But  suppose  you  sit  before  the  fire  of  a  fireplace.  The 
currents  are  all  rushing  toward  the  fire,  so  the  air  is  not 
bringing  heat  to  you.  You  are  not  touching  the  fire- 
place. Therefore  you  are  not  getting  heat  by  conduction. 
How  does  the  heat  get  to  you?  It  would  come  to  you 
whether  you  were  above  the  fire,  or  below  it,  or  on  one 
side,  just  as  the  light  of  a  lamp  does.  We  say  that  the 
heat  of  the  fire,  like  the  light  of  a  lamp,  is  radiated  to 
you.  Radiated  is  a  word  coming  from  radius,  meaning 
the  spoke  of  a  wheel.  The  heat  of  the  sun,  as  well  as  its 
light,  comes  to  us  by  radiation  through  space.  There 
are,  then,  two  ways  in  which  heat  can  come  to  us  from  a 
fire  :  (1)  by  conduction ;  (2)  by  radiation,  in  the  form  of 
"  heat  rays." 


64 


JUNIOR  SCIENCE 


60.  Hot-air  Furnace.  —  Sometimes  we  speak  of  the 
way  in  which  air  rises  when  heated  and  falls  when  cooled 
as  a  third  way  of  distributing  heat :  convection  (cf.  §  49). 
You  can  see  that  this  is  really  not  a  new  way  at  all,  be- 
cause in  order  that  there  may  be  warm  convection  currents 

in  the  air,  the  air  must 
be  heated  by  touching  a 
hot  body  (conduction)  or 
by  means  of  heat  rays 
(radiation). 

The  hot-air  furnace 
makes  use  of  the  principle  of 
convection  currents.  The 
air  is  heated  in  a  tight 
"drum  "  which  entirely  sur- 
rounds the  firepot  of  the 
furnace.  When  a  fire  is 
burning  in  the  firepot,  air 
currents  are  formed  in  the 
drum.  As  a  result,  warm 
air  rushes  up  through  the 
register,  rises  into  the  room, 
is  cooled,  falls  again,  and  goes  into  the  cold-air  register,  to 
be  taken  back  to  the  drum  to  be  reheated.  You  can  under- 
stand the  hot-air  furnace  better  if  you  will  study  Fig.  36. 
From  time  to  time  fresh,  outside  air  comes  through  the 
"  cold-air  intake  "  and  after  being  heated  is  distributed 
to  the  house. 

Do  you  think  there  are  convection  currents  in  a  re- 
frigerator? In  order  to  cool  the  whole  refrigerator, 


FIG.  36.  —  A  hot-air  furnace  is  a  fire 
pot  surrounded  by  a  "drum"  in  which 
air  currents  are  formed. 


HEATING   THE   AIR  OF    THE   HOUSE 


65 


where  should  the  ice  be 
placed,  near  the  bottom, 
or  near  the  top  ? 

61.  Heating  by  Hot 
Water.  -  -  By  examining 
a  hot-water  heating  sys- 
tem, you  will  find  that  it 
consists  of  radiators  in 
the  rooms  and  a  furnace 
in  the  basement  (Fig.  37). 
The  furnace,  instead  of 
being  surrounded  by  air, 
is  surrounded  by  a 
"  jacket "  of  water.  How 
is  the  heated  water  made 

f  .  i  FIG.  37.  —  A    hot-water   heating    sys- 

tO   move   irom    tne    Water     tem  depends  upon  the  convection  currents 

jacket  to  the  radiators  in   formed  in  the  water  surrounding  the 

firepot. 

the  rooms 

above?  We  can  carry  out  an  experi- 
ment which  will  help  us  to  understand 
this  process  (see  Fig.  38) . 

Into  a  glass  dish  (beaker  or  flask)  of  water  put  a 
little  sawdust  and  warm  the  dish  by  means  of  a 
small  flame  placed  under  it.  Follow  the  move- 
ments of  the  sawdust.  Are  there  convection  cur- 
rents in  the  water?  The  heated  water  acts  like 

FIG    38 The    heated  air.     It  is  lighter  than  water  of  the  ordinary 

sawdust  helps  us  to    temperature  and  rises  to  take  the  place  of  the 

see  the  convection    cooler  water  at  the  top.     Thus  you  see  that  the 
currents      in      the  , .  .  -,    i        .-, 

water  that  is  being    convection  currents  in  water  are  caused  by  the 

heated.  rising  of  warm  water  and  the  falling  of  the  cold 


66 


JUNIOR  SCIENCE 


water.     The  cooled  water  of  the   hot- water   heating   system   flows 
through  the  return  pipes  to  the  furnace,  to  be  heated  over  again. 

62.  What  is  Steam  Heating  ?  —  Examine  a  steam- 
heating  system.  In  a  hot-air  furnace,  the  air  is  heated 
and  then  circulated  by  convection  currents.  In  a  hot- 
water  system,  water  circulates  through  radiators  by 

convection.  In  the 
case  of  steam  heat- 
ing a  new  principle 
comes  into  play,  al- 
though the  steam 
heats  the  pipes  and 
the  heat  is  conducted 
to  the  air  and  radiated 
into  the  air  as  before. 
The  steam-heating 
system  (Fig.  39)  con- 
sists of  a  boiler,  con- 
taining water,  and  a 
furnace  to  give  heat. 
The  fire  in  the  furnace 
not  only  heats  the  water,  but  heats  it  so  much  that  the 
water  boils.  The  water,  then,  is  changed  from  a  liquid  into 
a  gas.  We  call  the  gas  ' '  steam. ' '  Steam  is  like  air,  but  with 
this  difference  :  the  steam  can  condense  easily  to  a  liquid. 
The  heat  used  to  boil  the  water  is  obtained  from  the 
burning  fuel.  This  heat  is  stored  away  in  the  steam, 
but  it  can  be  gotten  back,  if  the  steam  is  allowed  to  turn 
into  water.  Does  it  seem  strange  that  steam,  when  it 
condenses,  gives  off  heat? 


FIG.  39.  —  Steam-heated  houses  get  their 
heat  by  the  condensation  of  steam.  The  heat 
stored  in  the  steam  is  set  free  when  the  steam 
turns  into  water. 


HEATING   THE  AIR  OF   THE   HOUSE  67 

So  steam  at  100°  C.  could  enter  a  radiator,  and  water, 
also  at  100°  C.  could  leave  it,  and  yet  the  room  could  get 
a  great  deal  of  heat. 

Perform  this  experiment:  In  a  dish  (a  tin  can  or  deep  cup),  heat 
some  water  to  boiling  and  hang  a  thermometer  so  that  the  bulb  is  in 
the  water.  Let  it  boil  for  10  or  15  minutes,  until  a  considerable 
amount  has  boiled  away.  What  has  become  of  it?  From  time  to 
time  during  the  heating,  notice  the  reading  of  the  thermometer.  Does 
the  temperature  change  as  the  water  boils  away?  What  has  become 
of  all  the  heat  that  is  added  after  the  temperature  ceases  to  rise? 
The  answer  is  that  this  heat  is  used  to  change  the  liquid  water  into 
the  gas  form  of  water.  Now  when  the  steam  is  changed  back  to 
liquid  water,  as  it  is  in  the  radiators,  this  heat  appears  once  more, 
and  by  conduction  and  radiation  heats  the  air  of  the  room. 

63.  How  Can  We  Know  the  Temperature  of  the 
House?  —  By  the  temperature  of  any  object  we  mean 
its  degree  of  heat  or  cold.  Of  course  the  nerves  of  the 
skin  tell  us  something  of  temperature,  but  not  accurately 
enough.  If  we  want  to  keep  a  room  warm  to  please  an 
elderly  person,  we  are  likely  to  get  it  too  warm  for  the 
children.  The  best  temperature  for  the  air  of  a  house 
is  said  to  be  68°-70°  F.  Americans  living  in  cities, 
especially  in  apartments,  usually  have  the  rooms  too 
warm  for  health. 

Perform  the  following  experiment  to  see  how  easily  our  sense  of 
temperature  is  deceived:  Have  some  cold  water  hi  one  basin,  some 
lukewarm  water  hi  another,  some  hot  (not  scalding)  water  hi  another. 
Put  one  hand  into  the  cold  water  and  the  other  into  the  hot ;  then  put 
them  both  together  into  the  lukewarm  water.  To  the  cold  hand  the 
lukewarm  water  feels  hot,  to  the  warm  hand  the  lukewarm  water 
will  seem  cold.  Yet  both  are  your  own  hands  in  the  selfsame  basin 


68  JUNIOR  SCIENCE 

of  water.  Now  put  your  hands  on  some  oilcloth  and  on  a  rug ;  which 
is  the  colder?  The  oilcloth  seems  colder,  because  it  conducts  heat 
away  from  your  hand,  but  it  has  really  the  same  temperature,  since 
both  rug  and  oilcloth  are  in  the  same  room  and  exposed  to  the  same 
air.  To  get  an  accurate  temperature,  then,  we  cannot  depend  upon 
our  feelings,  but  must  use  a  thermometer. 

64.  How  Is  a  Thermometer  Made  ?  -  -  If  you  were 
given  the  problem  of  making  an  instrument  to  tell  tem- 
perature, how  would  you  set  to  work? 
We  have  learned  that  heat  expands  most 
substances,  while  cooling  contracts  them. 
Galileo  used  a  glass  bulb  filled  with  air 
and  a  small  tube  partly  full  of  water 
(Fig.  40).  As  the  air  of  the  bulb  became 
warmer,  it  expanded  and  pushed  the  water 
downward ;  if  the  bulb  was  cooled,  the  air 
FIG.  40.  -  shrank  and  the  water  went  higher  up  the 

?thermomeetaer.f     SlaSS    tube-       S°    he    COuld    tel1    whether    the 

temperature  rose  or  fell. 

Galileo's  thermometer  was  •  not  very  accurate,  but 
from  it  other  men  got  the  idea  of  measuring  temperature 
by  expansion  and  contraction  of  some  substance.  Fahren- 
heit used  a  glass  bulb,  as  Galileo  did,  but  instead  of  using 
air  in  the  bulb,  he  used  mercury.  This  is  a  liquid  metal 
which  expands  and  contracts,  although  not  as  much  as 
air  and  water  do.  The  tube  must  be  very  small  as 
compared  with  the  bulb.  Sometimes  alcohol,  which 
requires  an  extremely  small  tube,  is  used.  When  the 
thermometer  is  made,  the  bulb  is  blown  on  the  end  of 
the  tube,  and  the  bulb  and  a  little  of  the  tube  are  filled 


HEATING   THE  AIR  OF   THE  HOUSE 


69 


with  mercury.  The  bulb  is  then  heated  until  the  mer- 
cury fills  all  the  tube.  The  open  end  of  the  tube  is 
finally  sealed.  Modern  thermometers  are  "  graduated/' 
that  is,  marked  in  "  degrees. "  First  the  bulb  is  put 
into  melting  ice  (Fig.  41,  a),  and  the  place  at  which 
the  mercury  in  the  tube  stops  is  called  the  freezing  point, 
or  32°  F.  Then  the 
bulb  of  the  ther- 
mometer is  put  into 
steam  that  comes  off 
from  boiling  water 
(Fig.  41,  6) ;  this  place 
on  the  tube  is  the  boil- 
ing point.  It  is  marked 
212°  F.  Between  the 
freezing  point  and  boil- 
ing point  180  equal 
degrees  are  marked  off 


FIG.  41.  —  a.  The  "freezing  point"  of  a 
thermometer  is  obtained  by  putting  the  bulb 
in  melting  ice.  b.  The  "boiling  point"  is 
obtained  by  holding  the  thermometer  in  the 
steam  coming  off  from  boiling  water. 


(Fig.  42). 

65.  The  Two  Ther- 
mometer Scales. 
Some  years  after  Fah- 
renheit, another  scientist,  Celsius  (pronounced  Sel'si-us), 
called  the  freezing  point  0°  and  the  boiling  point  100° 
(Fig.  42).  His  thermometer  is  called  the  Centigrade 
thermometer ;  its  abbreviation  is  C.  You  can  see  that 
if  the  mercury  expands  and  contracts  evenly,  and 
if  the  glass  tube  has  the  same  bore,  or  opening, 
throughout  its  length,  we  can  mark  degrees  above  100° 
and  below  0°.  Thus,  if  we  make  a  mark  as  far  above 


70 


JUNIOR  SCIENCE 


100°  as  the  zero  mark  is  below  100°,  the  new  mark  will 
be  200°.  In  this  way  we  can  mark  mercury  thermometers 
up  to  the  temperature  at  which  mercury  boils  and 
down  to  that  at  which  it  freezes.  Why 
would  not  water  be  as  good  as  mercury  for 
a  thermometer? 

66.  Exercises. —  1.  Which  is  really  the  colder, 
a  metal  door  knob  or  the  wood  of  the  door  ?  Which 
feels  colder?  Why?  Do  your  woolen  mittens,  or 
your  rubbers,  feel  the  colder,  if  you  have  left  both 
out  of  doors?  Why? 

2.  .Why  can  ice  cream  be   carried   in   a   paper 
box  through  heated  air  and  yet  melt  very  little? 
Would  a  tin  box  keep  it  better?     Why  ? 

3.  Why   are   houses    built    with    double    walls 
having  an  air  space  between  the  walls  ? 

4.  Why  is  the  knob  on  the  cover  of  a  teakettle 
made  of  wood? 

5.  Why  does  ice  keep  through  the  summer  when 
packed  in  sawdust? 

6.  If  you  put  the  bowl  of  a  silver  spoon  into  a 
cup  of  hot  water,  the  handle  becomes  hot ;  explain. 
Would  the  handle  of  a  wooden  spoon  become  hot 
too?     Put  an  iron  ("  tin  ")  spoon  and  a  solid  silver 
spoon  into  a  cup  of  hot  water  at   the   same  time. 
Which  handle  becomes  hot  the  sooner?     Explain. 

7.  What  method  of  heating  is  used  in  your  house 
and  school  ?     Is  anything  done  to  keep  the  air  moist  ? 

8.  How  could  you  make  an  air  thermometer? 

.  9.  Should  steam  pipes  be  put  near  the  floor,  or  near  the  ceiling, 
in  order  to  heat  the  room  ?  Why  ?  Where  should  the  cold-brine  pipes 
be  put  in  a  cold-storage  room  in  order  to  cool  the  room?  Why? 

10.   What  are  some  of  the  advantages  and  disadvantages  of  the 
different  heating  systems? 


. 

C. 

V 

I00_ 

^212 

80- 

rr 

^170 

70- 

Ll«0 
Ll60 

00- 

LI*O 

Ll30 

SO- 

Ll20 

Ll  10 

4O_ 

poo 

80J 

L.  00 

20_| 

_70 

toJ 

LJiO 

L4O 

ol 

L=32 

J 

Lao 

iO_ 

Lio 

Lo 

2O_ 

LJO 

30- 

i_20 

40J 

L.4O 

1 

FIG.    42.  —  In 

the       Centigrade 

thermometer  the 

freezing  point   is 

called  0°  C.    and 

the  boiling  point 

100°  C. 

CHAPTER  IX 
MORE  ABOUT  HEAT 

67.  Are  Heat  and  Temperature  the  Same?  —  What 
is  the  temperature  of  any  object?     We  have  learned 
that  it  is  the  hotness  or  coldness,  or  degree  of  heat,  of 
the  object.     Boiling  water  has  a  temperature  of  100°  C. ; 
lukewarm  water  has  a  temperature  of  about  40°  C. ; 
cold  water  has  a  temperature  of  0°  to  10°  G.     It  makes 
no  difference,  when  you  are  speaking  of  the  temperature 
of  water,  how  much  water  you  have ;  a  cupful  of  boiling 
water  has  exactly  the  same  temperature,  or  degree  of 
heat,  as  a  pailful  has.     But  has  it  the  same  amount  of 
heat?     If  you  heat  water  over  a  gas  burner,  which  re- 
quires longer  heating,   the  cupful,   or  the  pailful?     Of 
course,  the  pailful  takes  the  longer  heating.     If  you  used 
the  water  to  warm  yourself,  which  would  give  you  the 
more  heat?     Of  course  the  pailful  would  give  you  the 
more.     In  a  house  heated  by  hot  water,  we  know  that  a 
large  room  requires  a  greater  amount  of  hot  water,  that 
is,  a  larger  radiator,  than  a  small  room  does.     From  all 
these  cases,  we  say  that  the  amount  of  heat  in  a  body 
depends  not  only  upon  the  temperature  of  the  body,  but 
also  upon  the  amount,  or  weight,  of  matter  in  the  body. 

68.  Can  Heat  Be  Measured?  — If  you  want  to  warm 
some  cold  water,  you  can  heat  it  over  a  fire,  or  you  can 
put  some  hot  water  with  it.     Is  there  any  way  of  know- 

71 


72  JUNIOR  SCIENCE 

ing  just  how  much  hot  water  to  use  in  order  to  heat  the 
cold  water  to  any  given  temperature?  If  you  mix  a 
pound  of  water  at  100°  C.  with  a  pound  of  water  at  0°  C., 
what  will  the  result  be?  You  will  have  two  pounds  at 
50°  C.  If  you  mix  1  pound  at  100°  C.  with  2  pounds  at 
0°  C.,  you  will  get  3  pounds  at  33  J°  C.  One  pound  at 
100°  C.  with  3  pounds  at  0°  C.  will  give  4  pounds  at  25°  C., 
and  so  on.  The  cold  water  gains  the  heat  which  the  hot 
water  gives  up. 

There  is  a  great  need  for  a  unit  of  heat,  so  that  we  can  speak  of  the 
quantity,  or  amount,  of  heat,  just  as  we  speak  of  the  amount  of  sugar 
or  iron.  The  amount  of  heat  that  is  needed  to  heat  a  pound  of  water 
through  one  degree,  Fahrenheit,  as  from  32°  F.  to  33°  F.,  is  called  a 
British  Thermal  Unit  (B.  T.  U.).  The  amount  of  heat  required  to 
heat  1  gram  of  water  through  one  Centigrade  degree,  as  from  15°  C. 
to  16°  C.,  is  called  a  calorie.  If  you  put  a  piece  of  hot  iron  into  1  gram 
of  water  and  heat  the  water  from  0°  to  10°  C.,  the  iron  adds  10  calories 
of  heat  to  the  water.  If  100  grams  of  water  at  10°  C.  are  put  into  an 
ice  box  and  cooled  to  0°  C.,  the  water  gives  off  1000  calories  of  heat  to 
the  ice  box.  Since  food  is  used  to  heat  the  body  and  to  enable  it  to  do 
work,  we  measure  the  value  of  food  in  calories. 

69.  Is  Heat  Needed  to  Melt  Ice  ?  —  What  becomes  of 
the  ice  in  an  ice  box  ?  It  melts.  What  causes  it  to  melt  ? 
Of  course  the  cause  is  the  heat  that  is  given  to  the  ice  by 
the  box  itself,  by  the  air  in  the  box,  and  by  the  food  that 
is  put  into  the  box.  As  these  give  their  heat  to  the  ice, 
they  themselves  are  cooled.  The  amount  of  heat  needed 
to  melt  1  gram  of  ice  is  able  to  heat  80  grams  of  water 
from  0°  C.  to  1°  C. ;  that  is,  80  calories.  It  is  because 
ice  takes  up  so  much  heat  in  being  changed  to  water 
that  it  cools  the  air  in  the  box  (cf.  Fig.  43).  People 


MORE  ABOUT   HEAT 


73 


often  speak  as  though  we  added  "  cold  "  to  the  food. 
Does  ice  conduct  or  radiate  "  cold  "?     When  we  think 
of  the  matter,  we  see  that  cooling  anything  is  not  adding 
"  cold  "   to  it,   but  taking  heat  from  it.     The  food  is 
cooled  because  it  gives  heat  to  the  ice.     By  losing  heat 
the  food  becomes  cold.     If  you  put  enough  chipped  ice 
into  water,  the   water  is   cooled  to    ^===========__ 

the  melting  point  of  ice,  that  is,  to 
0°  C.  Of  course  the  amount  of  ice 
needed  depends  upon  the  weight 
and  temperature  of  the  water. 

The  temperature  at  which  water  freezes 
is  the  same  as  the  temperature  at  which  ice 
melts.  So  we  put  a  thermometer  into  melting 
ice  (cf.  Fig.  41,  §  64)  to  mark  the  "  freezing 
point  "  on  the  thermometer.  The  tempera-  FIG.  43.  —  A  refrigerator 

ture  of  ice  and  the  water  it  forms  by  melting  isAb°!  f  which  f°°d  givej 

_&  off  heat  to  air  currents  and 

remain  at  0°  C.  until  all  the  ice  is  melted,  to    ice    and    so    becomes 

In  the  same  way,  when  water  freezes,  the  cooled.    Note   the   arrows 

i : ^ne        xi__ 


ice  and  the  water  remain  at  0°  C.  until  all  ™gs;   ™  ff*g« 


the  water  is  frozen. 


for  cold  air. 


70.  How  Does  the  Body  Keep  Its  Heat?  — First  let 
us  ask  how  the  body  gets  its  heat  ?  We  learned  in  §  46 
that  the  heat  comes  from  the  oxidation  of  our  food 
(cf.  Fig.  44).  The  excess  of  heat  produced  in  some  organs 
is  given  to  the  blood.  The  blood,  by  circulating  through 
the  body,  makes  the  temperature  of  the  body  nearly  the 
same  everywhere. 

Does  clothing  make  us  warm  or  cool?  You  will  see 
that  when  you  put  on  clothing  in  a  cold  room,  the  cloth- 


74 


JUNIOR  SCIENCE 


ing  has  the  same  temperature  as  the  room.  But  it  keeps 
your  body  warm  by  preventing  the  heat  of  the  body 
from  escaping.  If  you  wished  to  keep  a  piece  of  ice  from 
melting,  would  you  wrap  it  in  woolen  cloth,  or  in  cotton 
cloth?  Tramps  put  newspapers  inside  their  coats,  in- 
stead of  putting  on  overcoats.  Why?  Clothing  for 
preventing  the  escape  of  heat  from  the  body  should  be 

of  a  material  which  is  a  noncon- 
ductor of  heat. 

Wool  is  the  best  of  our  com- 
mon materials  for  warm  clothing. 
Woolen  goods  are  made  from  the 
natural  covering  of  sheep,  ani- 
mals which  live  through  very  cold 
winters  in  the  open.  The  feathers 
of  birds  keep  the  birds  warm,  not 
because  the  feathers  are  noncon- 
ductors of  heat,  but  because  they 
are  loose.  Did  you  ever  see 
birds  fluff  out  their  feathers  ?  By  doing  so  they  imprison 
a  great  deal  of  air  in  the  meshes  of  the  feathers.  It  is 
this  air  that  is  the  real  nonconductor  and  keeps  the 
bird  warm.  Linen  and  cotton  do  not  hold  so  much  air 
as  wool  and  are  therefore  better  heat-conductors  than 
wool.  They  make  better  clothing  for  summer  than  for 
winter. 

71.  Why  Does  Perspiration  Cool  the  Body?  — Per- 
form this  experiment :  Wet  your  hands  with  water 
having  the  temperature  of  the  room,  and  wave  them 
rapidly  to  and  fro,  until  the  water  has  evaporated.  Do 


FIG.  44.  —  What  becomes 
of  the  heat  we  obtain  from 
our  food? 


MORE  ABOUT  HEAT 


75 


they  feel  warmer  or  cooler  ?  Also  try  the  following : 
Put  a  few  drops  of  ether  or  gasoline  upon  your  hand  and 
blow  over  it  gently  until  the  liquid  has  evaporated. 
What  sensation  do  you  feel? 

From  these  experiments  you  can  see  that  evaporation 
of  liquids  takes  heat  from  bodies  touching  them  and  so 
'  causes  the  bodies  to  be  cooled.  This  is  what  perspira- 
tion does  for  our  bodies.  It  is  constantly 
evaporating  from  the  skin,  even  when  we 
do  not  know  it.  If  we  are  very  hot  from 
exercise,  the  perspiration  is  formed  more 
rapidly  than  it  can  evaporate  and  we  have 
"  noticeable  perspiration,'7  or  sweating. 
Heat  is  needed  to  produce  evaporation  of 
a  liquid,  just  as  it  is  to  cause  the  boiling 
of  a  liquid,  although  evaporation  takes 
place  at  a  lower  temperature.  The  heat 
which  is  needed  for  the  evaporation  is 
taken  from  the  body.  The  liquid  is 
changed  into  the  form  of  a  vapor,  or  gas, 
just  as  in  boiling. 

In  tropical  countries  a  porous  jar  is 
used  to  cool  water.  As  the  water  oozes  out  through  the 
walls  of  the  jar,  it  evaporates,  and  so  cools  the  water  that 
is  left  in  the  jar  (cf.  Fig.  45).  Would  you  say  that  the 
jar  should  be  left  in  a  draft,  or  where  the  air  is  quiet? 
Where  does  perspiration  evaporate  most  rapidly,  in  moving 
air  or  in  a  quiet  room? 

72.  Exercises. —  1.   Why   does   the   sprinkling   of   water   over   a 
porch  floor  cool  the  porch  in  hot  weather? 


FIG.  45.— 
As  water  oozes 
through  the  po- 
rous jar,  it  evap- 
orates and  cools 
the  water  inside 
the  jar. 


76 


JUNIOR  SCIENCE 


2.   If  you  have  a  cup  of  boiling  water,  what  is  tl  e  quickest  way  to 
cool  it?     What  becomes  of  the  heat? 

3.  Do  birds  and  other  animals  fluff  out  their 
feathers  and  fur  hi  summer,  or  in  winter?     Why? 

4.  Why  do  we  wear  cotton  and  linen  cloth- 
ing in  summer  and  woolen  clothing  in  winter  ? 

5.  Is  it  correct  to  say  that  woolen  clothing 
"  keeps  out  the  cold"? 

6.  Do  you  suppose  that  snow  and  ice  evapo- 
rate without  melting?      How   do  you   account 
for  the  fact  that  the  sharp  edge  of  a  piece  of  ice 
becomes  rounded,  even  in  very  cold  weather  ? 

7.  How    is     a    fireless     cooker    constructed? 
Wliy?     See  Fig.  46. 

8.  Is  a  fireless  cooker  also  a  "  heatless  "  cooker? 
What  is  the  source  of  its  heat  ? 

does   a   thermos   bottle   keep   hot   food   hot   and  cold 


FIG.  46.  —  A 
"fireless  cooker"  is 
a  box  made  of  non- 
conducting materi- 
als ;  it  does  not  allow 
the  heat  of  cooking 
food  to  escape. 


9.    Why 

food  cold? 


CHAPTER  X 
WEATHER 

73.  What  is  the  Weather?  — All  of  us  know  what 
weather  is.  It  is  the  temperature  of  the  air  outside  our 
houses ;  the  amount  of  moisture  in  the  air ;  whether  the 
sky  is  clear  or  cloudy ;  the  amount  of  dew  or  frost,  rain 
or  snow ;  the  direction  of  the  wind  and  the  rate  at  which 
it  is  moving.  These  are  the  things  which  we  mean  by 
"  the  weather."  The  average  of  the  weather  conditions 
at  any  given  place  makes  the  climate  of  that  place.  In- 
side our  houses  we  try  to  control  the  conditions  of  the 
air,  but  outside  our  houses  these  largely  control  us. 

The  weather  would  not  be  so  interesting  to  us  if  it 
were  always  the  same,  but  it  is  continually  changing. 
One  day  is  fair  and  the  next  stormy ;  one  is  hot  and  the 
next  cold ;  one  has  a  strong  wind  from  one  direction,  the 
next  has  a  wind  from  nearly  the  opposite  direction,  and 
the  third  has  no  wind  at  all.  So  the  expression,  "  change- 
able as  the  weather,"  is  a  common  one.  In  thinking 
about  the  weather  we  should  remember  that  we  are 
surrounded  on  all  sides  by  an  ocean  of  air :  the  atmos- 
phere. This  covers  the  earth  with  a  layer  perhaps  200 
miles  thick.  We  should  remember  that  the  weather  at 
the  place  where  we  live  is  the  condition  of  only  a  very 
small  part  of  the  atmosphere.  When  we  look  at  the 

77 


78  JUNIOR  SCIENCE 

weather  of  our  country  as  a  whole,  we  see  that  the  changes 
that  seem  to  be  haphazard  and  fickle  are  parts  of  great 
air  movements  and  that  there  is  a  cause  for  every  change. 

74.  Of  What  Is  the  Atmosphere  Composed?  — We 
have  already  learned  what  air  is  like.     It  has  weight  and 
takes  up  room,  like  a  liquid'  or  solid  object ;  it  can  be 
expanded  or  compressed.     We  have  also  learned  that 
it  is  made  up  of  more  than  one  kind  of  gas.     Its  active 
gas  is  oxygen,  which  is  used  in  burning  and  in  respiration  ; 
its  inactive  gas  is  chiefly  nitrogen.     Another  gas  that  is 
present  in  the  atmosphere  is  carbon  dioxide  (cf.  §42). 
Besides  these  gases  there  is  water  in  the  form  of  vapor. 
Water  vapor  is  taken  up  by  the  atmosphere,  as  the  water 
of  rains,  lakes,  and  rivers  evaporates.     Dust  is  also  found 
in  the  atmosphere;  it  contains  a  multitude  of  particles, 
some  living  and  some  not  living  (cf.  §  204). 

75.  What  Causes  Dew  and  Frost?  —  Have  you  ever 
seen  a  pitcher,   or  glass,   of  water  "  sweat  "  on  a  hot 
day?     Do  you  think  the  drops  of  water  go  through  the 
glass?     Suppose  we  perform  this  experiment  (Fig.  47) : 
Partly  fill  a  polished  metal  cup,  or  small,  smooth,  metal 
pail,  with  water  at  room  temperature  and  add  small 
pieces  of  ice  to  it,  one  at  a  time.     Add  a  new  one  only 
after  the  one  before  has  melted.     Stir  the  ice  and  water 
with  the  bulb  end  of  the  thermometer,  noting  carefully 
when  the  first  moisture  is  collected  on  the  outside  of  the 
metal  vessel.     Then  read  the  thermometer.     The  tem- 
perature you  find  is  the  dew  point  of  the  air  at  that  time. 
Find  it  on  a  day  when  the  weather  is  clear,  also  on  a 
rainy  day.     It  varies  according  to  the  amount  of  moisture 


WEATHER 


FIG.  47.  —  Thetem- 


in  the  air.  The  air  that  cannot  be  cooled  at  all  without 
depositing  dew  is  said  to  be  saturated  with  moisture,  or 
"  at  the  dew  point."  Dew  and  frost  are  water  deposited 
from  the  vapor  of  the  air  upon  cold  objects,  such  as  grass 
blades  and  stones.  These  objects  cool  more  rapidly  than 
air ;  so  they  cool  the  air  near  them,  causing  some  of  its 
water  to  be  condensed.  If  the  dew 
point  of  air  is  below  0°  C.,  frost  is 
formed  instead  of  dew. 

A  clear  night  favors  the  forming  of  dew  and 
frost,  because  the  earth  and  the  air  cool  more 
rapidly  in  clear  weather  than  when  clouds  are 
present.  Clouds  act  as  a  blanket  over  the 
earth  and  prevent  rapid  cooling.  A  gentle 
breeze  brings  fresh  supplies  of  air  to  the  cool 
objects  and  so  helps  in  the  formation  of  dew 
and  frost.  A  strong  wind,  however,  does  not 
leave  the  air  near  the  cool  object  long  enough 
to  allow  dew  or  frost  to  be  formed.  Orchards 
and  vineyards  in  hollows  are  more  likely  to 
be  injured  by  frost  than  those  on  a  hillside  or  on  the  hilltop,  because 
the  heavier,  cold  air  falls  into  the  hollows  and  remains  there.  Should 
orchards  be  planted  in  hollows? 

76.  How  Are  Clouds  Formed  ?  —  Some  people  think 
that  clouds  are  water  vapor  floating  in  the  air.  Is  this 
true?  In  the  first  place,  water  vapor  is  an  invisible 
gas,  like  the  air  itself.  In  the  second  place,  the  cloud 
particles  are  droplets  of  water  and  are  heavier  than  the 
air.  Why,  then,  don't  they  fall  to  earth?  The  answer 
is  that  they  do  fall,  but  that  at  a  certain  level,  which  forms 
the  bottom  of  the  cloud,  they  evaporate  completely  to 


moisture  begins  to 
appear  on  the  outside 
of  the  metal  cup  is  the 
"dew  point." 


80 


JUNIOR  SCIENCE 


form  the  invisible  water  vapor.  It  is  because  droplets 
are  formed  at  one  place  and  disappear  at  another  that 
clouds  change  their  forms  so  rapidly. 


(Copyright  by  International  Stereograph  Co.) 

FIG.  48.  —  Cumulus  clouds    are    great,    rounded    masses ;    cirrus    clouds    are 
feathery  or  streaky. 

If  the  water  vapor  in  the  air  just  above  the  ground  is 
condensed  to  droplets,  we  have  a  fog.  If  this  happens 
some  distance  above  the  earth,  we  have  clouds.  Clouds 


WEATHER  81 

are  often  formed  because  ascending  air  currents  loaded 
with  water  vapor  meet  cooler  currents  and  are  cooled 
below  the  dew  point.  If  the  sun's  heat  raises  the  tem- 
perature of  the  air  above  the  dew  point,  fogs  and  clouds 
evaporate  and  disappear.  Some  clouds  consist  of  ice 
particles. 

Observe  the  clouds  and  see  how  wonderful  they  are,  and  how  many 
different  shapes  they  have.  Some  are  rounded,  like  heaps  of  wool ; 
these  are  called  cumulus  clouds  (Fig.  48).  They  are  formed  by 
ascending  air  currents.  "  Thunderheads  "  are  one  form  of  cumulus 
clouds.  They  are  one  or  more  miles  high. 

Cirrus  clouds  are  feathery,  or  made  of  distinct  lines.  They  are  the 
highest :  often  five  miles  above  the  earth  (Fig.  48). 

Stratus  clouds  are  in  layers.    They  are  about  \  to  3  miles  high. 

Nimbus  clouds  are  like  great  dark  "  veils."  They  are  cumulus  or 
stratus  clouds  depositing  rain  or  snow  (Fig.  53,  §  80). 

77.   Why  Do  We  Have  Rain,  Snow,  and  HaU?  —  You 

know  how  different  rains  can  be :  sometimes,  the  rain 
falls  in  tiny  drops,  at  other  times  in  great  splashes. 
Snow  is  often  made  up  of  tiny  grains  and  again  of  large, 
fluffy  flakes.  How  large  the  raindrops  shall  be  depends 
upon  how  the  droplets  are  condensed.  Raindrops  are  made 
up  of  a  large  number  of  cloud  droplets  united.  These 
big  drops  fall  through  the  air  and  reach  the  earth  before 
they  can  be  evaporated.  If  the  condition  of  the  air  is 
right  for  a  rain,  but  the  temperature  is  below  0°  C.,  we 
have  snow  (Fig.  49). 

Hail  is  made  up  of  layers  of  ice  and  snow.  At  the 
center  there  is  probably  a  frozen  raindrop.  The  frozen 
drops  are  carried  upward  by  air  currents ;  then  they  fall 


82  JUNIOR  SCIENCE 

down  some  distance  and  are  carried  up  again,  until  they 
take  on  many  layers.  Finally  they  are  too  heavy  for 
the  air  currents  to  support,  so  they  fall  as  hail.  Hail  does 
a  great  deal  of  damage  to  window  panes,  trees,  and  crops. 
78.  What  is  Rainfall  ?  —  Rain  is  so  necessary  for  crops, 
that  its  amount  is  very  important  to  a  country.  If  you 


(Courtesy  of  the  Mclntosh  Stereopttcon  Co.) 
FIG.  49.  —  The  delicate  lines  of  snowflake  and  frost. 

examine  a  rainfall  map  of  our  land  (Fig.  50),  you  will 
find  that  one  region  gets  less  than  10  inches  of  rain  in  a 
year;  while  another  region  gets  60  inches,  and  another 
even  80  or  100  inches.  Before  this  map  could  be  made, 
the  rainfall  had  to  be  measured  for  many  years.  Rain 
is  caught  in  a  rain  gauge  (Fig.  51).  The  opening  of  the 


WEATHER 


83 


FIG.  50.  —  The  figures  show  how  much  rain,  on  the  average,  falls  each  year 
in  different  regions  of  the  United  States. 

funnel  is  made  just  10  times  as  large  as  the  cross 
section  of  the  stem,  so  that  TV  of  an  inch  of  rain  makes 
a  depth  of  1  inch  in  the  stem. 

Make  a  simple  rain  gauge  by  putting 
a  baking  powder  can  in  the  yard  and 
measuring  the  depth  of  water  in  it  after 
a  hard  rain.  Keep  a  record  of  every 
rainfall  for  a  month  or  so.  Gauge 


Snow  is  measured  as  rain,  the  snow  being 
allowed  to  melt.  When  we  remember  that  more 
than  half  the  earth  has  less  than  20  inches  of 

rain  in  a  year  and  has,  therefore,  not  enough  for 

of  the  funnel  is  ten 
farming,  we  see  why  the  rainy  regions  have  been     times   as    large 
more    thickly    settled    by   man.    The    greatest     that  of  the  stem. 


FIG.  51.  —  A  rain 
gauge.    The  opening 


84  JUNIOR  SCIENCE 

rains  are  in  India,  where  the  average  is  500  inches  a  year.  In 
deserts  there  may  be  only  5  inches  a  year.  The  great  rains  of  India 
are  due  to  the  moist,  warm  winds  that  blow  from  the  Indian  Ocean. 
As  the  winds  rise  higher  and  higher  above  sea  level  and  are  cooled  more 
and  more,  they  deposit  their  moisture.  After  they  have  passed  the 
Himalayas,  they  are  dry  winds  and  blow  over  a  land  which  is  a  desert. 
Why  are  there  heavy  rains  on  the  coast  of  Washington,  Oregon,  and 

northern  California, 
and  such  light  ones 
farther  east  ?  Why 
is  there  such  a  heavy 
rainfall  on  the  south- 
ern coast  of  the  United 
States? 

79.  What    are 
the    Winds  ?- 
Have    you    seen 

FIG.  52.  —  Air  currents  over  a  fire,  or  over  the  ^ 

heated  earth,  rise  to  a  certain  height,  then  flow  out  the  SHloke  and 
horizontally,  and  finally  fall  again  to  the  earth  as  -i  r 

they  become  cooled.     Tell  why.  Sparks 

large  bonfire  on  a 

quiet  evening  ?  They  rise  almost  vertically  and  then  move 
out  horizontally  before  they-come  down  (Fig.  52).  If  we 
could  follow  the  currents  of  air  near  the  fire,  we  would  find 
that  the  air  is  flowing  along  the  ground  toward  the  fire,  to  take 
the  place  of  that  which  ascends.  Thus  we  get  a  complete 
circulation  of  air,  because  some  of  it  is  heated  by  the  fire. 
We  do  not  feel  the  currents  that  ascend,  nor  the  currents 
that  descend,  but  we  feel  those  that  flow  along  the  ground. 
Such  horizontal  air  currents  are  the  winds.  The  air  is 
very  free  to  move,  and  if  the  air  pressure  becomes  smaller 
at  any  given  place,  the  heavier  air  around  that  place 
crowds  in  from  all  sides  and  pushes  the  lighter  air  up. 


WEATHER  85 

The  force  with  which  the  wind  will  blow  depends  upon 
the  pressure.  The  greater  the  difference  in  pressure  be- 
tween two  places,  the  more  rapidly  the  wind  will  blow 
from  one  to  the  other. .  We  should  expect  this  to  be  so, 
since  we  know  that  water  will  flow  more  rapidly  down  a 
steep  grade  than  down  a  gentle  one. 

A  light  wind  is  one  which  just  moves  the  leaves  of  trees.  Its 
velocity,  or  rate,  is  10  miles  an  hour  or  less. 

A  high  wind  sways  trees ;  it  moves  25  to  40  miles  an  hour. 

A  gale  is  air  rushing  along  at  40  to  60  miles  an  hour. 

In  a  hurricane  or  a  tornado  the  air  moves  above  60  miles  an  hour ; 
it  may  even  go  as  high  as  200  or  more. 

Over  the  ocean  there  are  regular  winds  that  blow  for  months  at  a 
time ;  such  are  the  prevailing  westerlies  of  temperate  zones  and  the 
monsoons  of  the  Indian  and  Pacific  Oceans. 

Carry  out  the  following  experiment :  Fill  one  saucer 
with  dry,  black  earth  and  fill  another  with  water.  Let 
both  stand  until  they  come  to  the  temperature  of  the 
room;  then  set  them  side  by  side  in  the  sunlight. 
With  a  thermometer  tell  which  is  warmed  the  more 
rapidly. 

Land  breezes  and  sea  or  lake  breezes  are  due  to  the 
fact  that  the  earth  is  heated  more  by  day  than  the  water 
is,  and  is  cooled  more  at  night.  Because  of  this  fact, 
ascending  currents  rise  over  the  land  during  the  day  and 
over  the  water  at  night.  When  the  heated  air  current 
rises  over  the  land,  a  horizontal  current  of  air  flows  in 
from  the  sea.  Thus  we  have  a  sea  breeze  during  the 
day.  At  night  the  wind  blows  from  the  land  to  the  sea 
(the  land  breeze). 


86 


JUNIOR  SCIENCE 


80.  What  Causes  Our  Great  Storms  ?  -  -  You  already 
know  one  of  the  effects  of  the  rotatiod  of  the  earth  on 
its  axis :  it  causes  day  and  night.  It  also  has  a  great 
deal  to  do  with  the  winds.  If  the.  earth  were  not  turning, 

the  winds  would  blow 
toward  the  place  hav- 
ing a  low  pressure, 
much  as  they  do  now, 
but  they  would  blow 
directly  there,  in  a 
straight  line,  just  as 
the  spokes  of  $,  wheel 
come  together  at  the 
hub.  But  the  rota- 
tion of  the  earth  on 
its  axis  causes  the 
winds  to  blow  toward 
the  "  low  "  region  in 
a  curve,  hence  the 
A  whirling  mass  of  air 


FIG.  53.  —  In  a  lightning  discharge  the  elec- 
tricity bursts  through  the  air  and  passes  from 
cloud  to  cloud  or  between  clouds  and  the  earth. 

air  at  the  center  is  set  to  whirling. 


doing  this  on  a  small  scale  is  called  a  whirlwind. 

In  a  cyclone  the  whirling  mass  of  air  may  be  1000  miles  in  diameter 
and  5  miles  high.  In  the  northern  hemisphere  the  air  is  set  whirling  in 
a  direction  opposite  to  the  movement  of  the  hands  of  a  clock ;  in  the 
southern  hemisphere  the  whirl  is  in  the  direction  in  which  the  hands 
of  a  clock  move.  In  the  northern  United  States  the  whole  area  of 
low  pressure  moves  easterly  at  the  rate  of  about  30  miles  an  hour. 

Our  cyclones  are  not  tornadoes,  but  the  "  cold  waves  " 
that  sweep  down  upon  us  more  or  less  regularly  in  both 
winter  and  summer. 


WEATHER 


87 


Thunderstorms  are  smaller  storms  in  the  great  cyclones.  They 
usually  come  after  very  warm  weather.  The  lightning  (Fig.  53)  that 
comes  with  them  consists  of  great  electric  sparks  (cf.  §  2).  It  is 
formed  by  the  rapid  condensation  of  water  vapor  on  a  large  scale. 
The  lightning  passes  from  cloud  to  cloud,  or  between  clouds  and  the 
earth.  Thunder  is  the  vibrations  produced  in  the  air  as  the  lightning 
flashes  through  it.  From  the  time 
it  takes  for  us  to  hear  the  thunder 
caused  by  a  flash  of  lightning,  do 
you  judge  that  sound  travels  more, 
or  less,  rapidly  than  light  ? 

Tornadoes,  or  "  twisters  "  (Fig. 
54),  are  whirling  masses  of  air  from 
50  feet  to  half  a  mile  in  diameter. 
The  air  pressure  at  the  center  may 
be  as  low  as  7  or  8  pounds  to  the 
square  inch,  and  toward  this  center 
the  wind  may  blow  as  rapidly  as 
200  miles  an  hour.  The  tornado 
can  pick  up  bowlders,  cut  houses  in  two  as  a  great  knife  would, 
and  can  turn  locomotives  over.  Frail  objects,  such  as  straws,  may  be 
driven  into  oak  wood. 

When  seen  coming,  a  tornado  looks  like  a  heavy  cloud  shaped  like  a 
funnel.  The  lower  end  dangles  along  the  ground,  touching  it  here  and 
there.  Our  tornadoes  move  northeastward  at  25  to  40  miles  an  hour. 

Hurricanes  are  violent  storms  that  arise  in  the  Atlantic  off  the 
northern  part  of  South  America.  Similar  storms  in  the  Indian  and 
Pacific  Oceans  are  called  typhoons.  They  are  whirling  masses  with  a 
diameter  of  300  miles  or  more,  and  having  very  violent  wind  and 
ram.  The  West  India  hurricanes  move  northwest  until  they  reach 
the  southeastern  coast  of  the  United  States;  then  they  move  north- 
east and  finally  into  the  Atlantic.  They  come  in  the  summer  and 
cause  great  damage  to  'life  and  shipping.  Not  only  do  they  bring 
wind  and  ram,  but  also  great  storm  waves  that  sweep  over  the  low 
portions  of  the  coast. 


FIG.  54.  —  How  a  Western  "  twister  " 
looks  when  it  goes  into  action. 


88 


JUNIOR  SCIENCE 


11  S.  Department  of  Agricull 
WEATHER    BUREAU 


ItUTfc 


U  S.  Department  of  Agricultures 
WEATHER    BUREAU 

W11XI5  L.  MOORE. 


WEATHER 


89 


FIG.  55.  —  Figs.  55,  a,  6,  and  c,  are  weather  maps  of  three  successive  days. 
Note  the  "low"  area  has  moved  to  the  northeast.  The  arrows  show  the  direc- 
tions of  the  wind.  The  first  figures  beside  the  arrows  show  the  temperature ; 
the  second  figures  show  the  rainfall  in  inches  during  the  preceding  24  hours; 
the  third  figures  (if  present)  show  the  wind's  velocity.  Other  signs  are : 

O  clear  ;  ®  partly  cloudy  ;   •  cloudy  ;  (R)  rain  ;  ©  snow  ;  (M)  report  missing. 

81.  What  is  the  Weather  Service?  —  Did  you  ever 
visit  a  weather  office?  If  you  did,  you  found  there 
delicate  instruments  for  recording  the  direction  and 
velocity  of  the  wind  and  for  measuring  the  rainfall,  the 
temperature,  the  atmospheric  pressure,  and  the  amount 
of  water  vapor  in  the  air.  These  facts  are  recorded  each 
day  at  8  A.M.  on  the  Atlantic  coast  and  at  5  A.M.  on  the 
Pacific  coast ;  they  are  then  telegraphed  to  Washington. 
When  all  the  results  are  put  together  on  a  weather  map 
(Fig.  55),  they  give  the  expert  at  Washington  an  in- 


90  JUNIOR  SCIENCE 

stantaneous  photograph  of  the  weather  of  the  whole 
country.  From  this  map  the  expert  can  tell  not  only 
what  the  weather  is,  but  what  it  is  likely  to  be,  for  he 
can  tell  where  the  low  areas  are,  in  what  direction  they 
are  traveling,  whether  rain,  snow,  or  frost  are  on  the 
way,  whether  it  will  be  hot  or  cold.  The  coming  of  cold 
waves,  or  of  storms  that  will  injure  shipping  or  cause 
floods  on  rivers,  can  be  foretold  in  this  way.  Sometimes 
there  is  a  mistake,  because  storms  do  not  all  act  exactly 
the  same,  but  usually  the  predictions  are  accurate,  and  they 
save  many  lives  and  many  millions  of  dollars  annually. 

When  the  weather  expert  thinks  a  cold  wave  is  coming, 
he  sends  word  to  the  cities  of  that  region,  and  from  these 
cities  warnings  are  sent  out  by  telephone  to  shippers  and  to 
farmers.  Signs  are  also  placed  on  trains,  so  that  farmers 
are  warned  to  do  all  they  can  to  save  crops.  In  a  similar 
way  warnings  of  coming  storms  are  sent  to  ship  captains. 

Weather  Maps.  —  On  a  weather  map  you  will  see  heavy  solid  lines 
joining  places  that  have  the  same  atmospheric  pressure  in  a  given 
region ;  these  are  called  isobars.  We  can  see  from  the  map  that  the 
isobars  curve  irregularly  about  the  regions  of  low  pressure  and  high 
pressure.  The  "  lows  "  show  cyclonic  storms.  The  "  highs  "  bring 
the  sharp,  bright  weather  which  follows  storms.  There  are  also  dotted 
lines  to  join  places  having  the  same  temperature ;  these  are  isotherms. 
Generally  only  the  isotherms  for  freezing  and  for  zero  weather  are 
shown.  The  map  shows  also  the  temperature  of  the  weather  stations  of 
the  country,  the  direction  of  the  wind,  and  the  amount  of  rain  or  snow. 

82.  Exercises. —  1.  Examine  weather  maps  for  several  successive 
days.  In  what  general  direction  do  the  "  lows  "  move? 

2.  What  is  a  weather  vane?  Its  shape?  Why  does  it  have  this 
shape? 


WEATHER  91 

3.  Fishermen  on  the  seacoast  often  sail  out  at  or  before  daybreak 
and  return  about  noon.     Do  the  land  and  sea  breezes  help  or  hinder 
them? 

4.  Find  out,  if  you  can,  what  are  the  various  flags  used  as  weather 
signals. 

5.  Why  do  men  say,  "If  the  wind  doesn't  '  come  up '  tonight, 
we  shall  have  frost  "? 

6.  Why  are  weather  forecasts  valuable? 

7.  What  is  the  force  which  makes  great  waves  rush  up  on  a  beach? 

8.  What  is  the  difference  between  the  terms  weather  and  climate? 

9.  Why  do  we  have  hail  in  the  summer  time,  but  do  not  have 
snow? 

10.  Suppose  you  were  watching  a  barometer  while  a  tornado  passed 
near  you,  what  should  you  observe  ? 

11.  Did  you  ever  watch  a  miniature  tornado,  or  whirlwind?    De- 
scribe it. 


PART  III 
MATTER  AND  ENERGY  IN  EARTH  AND  SKY 


CHAPTER  XI 
THE  HEAVENLY  BODIES 

83.  What  is  the  Earth  Like?  — We  like  to  think  of 
our  earth  as  a  great,  solid  floor  on  which  we  stand  and 
on  which  we  can  depend.  We  speak  of  getting  down  to 
the  firm  earth.  But  if  we  wish  to  get  a  correct  idea  of 
what  our  earth  is  like,  we  must  imagine  ourselves  as 
standing  off  in  space  and  looking  back  at  the  earth.  Then 
we  shall  see  it  as  a  great,  round  ball  turning  with  dizzy 
speed  from  west  to  east  and  flying  with  still  dizzier  speed 
in  its  great  path  around  the  sun. 

The  ancient  Greeks  knew  that  the  earth  is  round  and 
that  it  turns  or  rotates.  They  had  even  worked  out  a 
way  of  calculating  its  size,  but  their  work  was  afterwards 
forgotten.  So  it  came  about  that  when  Columbus,  in  the 
latter  part  of  the  fifteenth  century,  said  that  our  earth 
is  a  great  ball,  the  people  of  his  day  made  fun  of  him. 
As  we  know,  the  time  the  earth  takes  for  one  rotation 
is  a  day.  The  imaginary  line,  or  axis,  around  which 
the  earth  spins,  passes  through  the  north  and  south  poles. 

With  a  tapeline  measure  carefully  the  distance  around 
(the  circumference  of)  a  round  plate,  or  hoop,  or  wheel ; 
then  measure  the  distance  across  it,  through  the  center 
(the  diameter) .  How  many  times  as  great  as  the  diameter 
is  the  circumference?  Then  measure  the  circumference 

95 


96  JUNIOR  SCIENCE 

of  a  tennis  ball,  or  croquet  ball,  or  baseball,  and  calculate 
its  diameter. 

By  very  careful  measurement  men  have  found  that 
the  circumference  of  the  earth  at  the  equator  is  nearly 
25,000  miles.  What,  then,  is  its  diameter? 

How  rapidly  must  a  spot  at  the  equator  be  turning? 
Do  you  see  that  it  must  turn  through  about  25,000  miles 
in  24  hours,  or  at  the  rate  of  about  1000  miles  an  hour? 

We  may  give  the  earth's  rate  of  rotation  in  another  way : 
We  know  that  the  distance  around  a  circle  may  be  measured  in 
degrees,  each  complete  circle  having  360  degrees  (written  360°).  The 
distance  around  a  sphere  like  the  earth  is  measured  on  a  circle  that 
passes  around  it,  and  is  also  stated  in  degrees.  Since  the  earth  spins 
about  on  its  axis  once  in  every  24  hours,  in  one  hour  it  goes  through 
360^-24,  or  15  degrees. 

84.  What  is  the  Sky?  —  Have  you  ever  looked  along 
a  straight  picket  fence  and  observed  that  the  pickets  all 
seem  to  be  at  about  the  same  place?  Yet  our  judgment 
tells  us  that  they  are  one  behind  the  other.  Perhaps 
you  have  noticed  how  hard  it  is  to  tell  which  of  a  group 
of  mountain  peaks  are  near  and  which  are  farther  away. 
All  distant  objects  seem  to  be  at  about  the  same  distance 
from  us.  So  it  is  with  the  sky.  The  sky  seems  to  be  a 
hollow  sphere  and  the  heavenly  bodies  all  seem  to  move 
across  its  surface.  Yet  the  truth  is  that  some  of  these 
bodies  are  enormously  distant  as  compared  with  others. 
When  we  see  the  moon  near  a  certain  bright  star,  their 
nearness  to  each  other  is  due  to  the  fact  that  they  are  in 
the  same  direction  from  us,  one  beyond  the  other.  Just 
in  the  same  way  the  sun  and  moon  at  intervals  of  about 


THE  HEAVENLY  BODIES 


97 


four  weeks  seem  to  be  almost  at  the  same  place  in  the  sky 
(the  time  of  "  new  moon  "),  although  the  sun  is  much 
farther  away  than  the  moon. 

While  it  is  true  that  the  sky  is  just  a  make-believe 
sphere,  we  must  learn  its  parts  if  we  want  to  study  the 
heavenly  bodies.  The  circle  in  which  the  sky  and  earth 


i  Spring  nnd 
I     autumn 


sunset 


FIG.  56.  —  The  path  of  the  sun  across  the  sky  in  the  four  seasons  of  the  year. 
When  is  the  sun  above  the  horizon  for  the  longest  time  ?  The  shortest  ?  (Sug- 
gested by  Todd's  Astronomy.) 

seem  to  meet  is  the  horizon  (Fig.  56).  It  is  the  line 
beyond  which  we  cannot  look  because  the  bulging  sur- 
face of  the  earth  is  in  the  way.  The  horizon  has  its  four 
points :  north,  east,  south,  and  west.  The  point  in  the 
sky  exactly  above  you  is  the  zenith. 

85.   Why  Do  the  Heavenly  Bodies  Rise  and  Set?- 
As  you  look  at  the  sky,  you  see  that  the  moon  and  the 
stars,  like  the  sun,  rise  in  the  east  and  set  in  the  west. 


98  JUNIOR  SCIENCE 

Men  used  to  suppose  that  all  these  bodies  turned,  or 
revolved,  about  the  earth,  but  we  now  have  many  proofs 
that  the  earth  is  turning,  or  rotating,  on  its  axis  once 
every  24  hours,  and  that  it  is  this  rotation  of  the  earth 
that  brings  us  back  each  day  to  such  a  position  that  we 
can  again  begin  to  see  the  same  heavenly  bodies.  This 
is  what  we  mean  by  the  rising  of  the  heavenly  bodies. 
If  you  were  walking  up  a  hill,  behind  which  there  is  a 
church,  the  church  might  seem  to  rise  when  you  could 
begin  to  see  its  steeple,  although  what  is  really  happening 
is  that  you  are  moving  toward  the  church  and  the  church 
is  standing  still.  When  you  move  away,  the  church 
seems  to  "  set.7' 

Watch  the  path  of  the  sun  across  the  sky.  Does  the 
sun  rise  exactly  at  the  east  point  of  the  horizon  ?  It  does 
so  only  twice  a  year  :  in  March  and  in  September.  You 
know  that  in  early  summer  the  sun  rises  far  north  of  the 
east  point  and  sets  far  north  of  the  west  point ;  at  this 
time  it  shines  into  the  north  windows  of  our  houses 
(Fig.  56).  In  winter,  on  the  other  hand,  the  sun  rises 
far  south  of  the  east  point  and  sets  far  south  of  the  west 
point. 

86.  What  is  the  Path  of  a  Star  across  the  Sky?- 
Are  there  any  stars  that  do  not  rise  and  set,  but  are 
always  above  the  horizon?  If  you  look  at  the  northern 
sky  on  a  bright  night,  you  will  see  the  Big  Dipper. 
This  is  a  group,  or  constellation,  of  seven  principal  stars. 
The  two  bright  stars,  which  make  one  side  of  the  bowl  of 
the  dipper,  point  toward  the  North  Star  and  are  known 
as  the  "  Pointers.77  If  you  live  in  the  northern  states 


THE   HEAVENLY   BODIES  99 

and  watch  the  position  of  the  Dipper  at  a  given  time  — 
say  at  8  P.M.  —  every  week  or  two  during  several  months, 
you  will  find  that  it  revolves  about  the  North  Star  in  a 
complete  circle  and  is  always  above  the  horizon.  If  a 
star  is  somewhat  farther  away  from  the  North  Star  than 
the  Dipper  is,  it  will  be  above  the  horizon  part  of  the 
time  and  below  it  part  of  the  time ;  that  is,  it  will  rise 
and  set.  The  North  Star  is  also  called  Polaris. 

The  stars  that  keep  their  positions  with  respect  to 
one  another,  so  that  they  can  always  be  found  in  a  given 
constellation,  are  called  fixed  stars. 

If  you  were  at  the  equator,  all  the  stars  would  rise 
and  set  and  their  paths  would  all  be  perpendicular  to 
the  horizon.  The  North  Star  would  be  just  at  the 
horizon.  Why  is  this?  You  must  remember  that  the 
daily  motions  which  the  stars  seem  to  have  are  due  to 
the  turning  of  the  earth  and  that  the  north  pole  of  the 
earth  always  points  to  the  north  pole  of  the  sky.  This 
makes  all  the  stars  seem  to  revolve  around  the  north  pole 
of  the  sky.  The  sky's  north  pole  is  near  the  North  Star. 

87.  What  are  Some  Star  Groups  ?  —  We  have  already 
learned  of  one  star  group,  or  constellation,  called  the 
Big  Dipper.  This  is  part  of  a  larger  group  called  the 
Great  Bear.  If  you  try  to  make,  out  the  shape  of  the 
Great  Bear,  you  will  need  a  great  deal  more  imagination 
than  to  find  the  Dipper.  Many  of  the  constellations 
received  their  names  centuries  ago  from  the  Egyptians, 
the  Greeks,  or  the  Arabs  ;  others  are  more  modern.  The 
stars  and  constellations  made  out  by  the  ancients  were 
named  after  heroes,  animals,  or  events. 


100  JUNIOR  SCIENCE 

The  Dipper  is  only  one  of  several  constellations  near 
the  North  Star.  Another  one  is  the  Little  Dipper;  this 
is  a  part  of  the  Little  Bear.  The  North  Star  is  at  the 
end  of  the  Little  Dipper's  handle,  or  at  the  end  of  the 
Little  Bear's  tail.  See  the  star  map  (Fig.  57,  a  and  6)  in 
this  chapter. 

Let  us  look  for  another  constellation.  Imagine  a  circle 
in  the  northern  sky  and  that  the  North  Star  is  at  its 
center ;  also  imagine  that  the  circle  passes  through  the 
Big  Dipper  Look  on  the  opposite  side  of  the  circle  and 
you  will  find  the  pretty  group  called  Cassiopeia.  It 
looks  like  a  chair. 

Probably  our  most  beautiful  group  of  constellations 
is  .the  one  seen  in  the  east  in  the  early  evening  during 
November  and  December.  It  is  made  up  of  the  Pleiades, 
a  brilliant  cluster,  followed  by  the  red  star,  Aldebavan, 
in  the  eye  of  Taurus,  the  Bull.  Behind  these  and  a  little 
farther  south  is  Orion,  with  his  belt  of  three  bright  stars 
and  his  sword  of  three  fainter  ones.  After  Orion  comes 
the  Great  Dog  (Canis  Major)  with  the  Dog  Star,  Sirius. 
This  is  the  brightest  fixed  star  of  the  sky. 

The  Galaxy,  or  Milky  Way,  is  a  belt  of  light  which 
passes  across  the  heavens.  The  telescope  shows  us  that 
it  is  made  up  almost  entirely  of  separate  stars,  each  too 
small  to  be  seen  by  the  eye  alone. 

88.  How  Far  Away  are  the  Stars  ?  —  The  brightness 
of  the  stars  depends  upon  how  much  light  they  give  off 
and  also  upon  how  far  away  from  us  they  are.  The  star 
Sirius  gives  off  40  times  as  much  light  as  our  sun,  but  it 
is  enormously  farther  away.  For  distances  on  the  earth, 


THE   HEAVENLY,   J}OT)JRS,  ,      101 

the  mile  (5280  feet)  is  the  unit,  but  how  little  we  are  able 
to  understand  the  distance  to  the  sun,  when  some  one 
says  that  it  is  about  93,000,000  miles  away !  A  train 
traveling  a  mile  a  minute  would  need  about  178  years  to 
go  from  the  earth  to  the  sun.  Light  travels  about 
186,000  miles  a  second,  yet  even  light  requires  499  seconds 
(over  8  minutes)  to  reach  us  from  the  sun. 

If  we  think  the  sun  is  far  away,  then  what  shall  we 
say  of  the  distance  to  the  nearest  fixed  star,  the  light  of 
which  requires  between  three  and  four  years  to  reach 
us?  Can  you  realize  the  distance  to  the  North  Star 
when  you  are  told  that  the  light  that  comes  to  our  eye 
tonight  left  the  star  at  least  47  years  ago  ? 

89.  Why  are  Some  Heavenly  Bodies  Wanderers  ?  - 
As  we  have  learned,  the  stars  in  a  constellation  hold 
their  places,  but  the  constellations  themselves  seem  to 
move  around  the  sky  from  east  to  west  once  each  day. 
They  seem  to  do  this  because  the  earth  rotates  from  west 
to  east.  There  is  another  important  change  in  the  con- 
stellations. If  we  watch  one  of  them,  such  as  the  Pleiades, 
from  month  to  month,  we  shall  see  that  it  rises  earlier 
and  earlier  each  evening ;  until  at  the  end  of  six  months, 
instead  of  rising  in  the  east  at  sunset  it  now  rises  and 
sets  with  the  sun.  Then  we  cannot  see  it  at  all,  because 
the  sun  makes  a  much  brighter  light.  After  six  months 
the  constellation  again  rises  at  sunset.  Another  way  of 
saying  this  is  that  the  sun  is  a  "  wanderer  "  and  moves 
eastward  among  the  stars.  First  it  is  in  one  constella- 
tion, then  in  another  farther  east,  until  it  has  gone  en- 
tirely around  the  heavens  in  a  great  circle. 


FIG.  57,  a  and  b.  —  Fold  the  inner  margin  of  the  page  so  that  the  halves 
hold  the  map  so  that  the  North  Star  of  the  map  is  directed  toward  the  North 
of  the  map ;  the  stars  will  then  appear  somewhat  as  they  should  be  at  about 
from  the  pole.  (Suggested  by  Young's  Astronomy.) 

102 


The  Dipper 
* 


fe* 

l*tlj. 


of  the  map  come  together.  Grasp  the  book  with  both  hands,  face  north  and 
Star  of  the  sky.  Turn  the  map  so  that  the  present  month  shall  be  at  the  top 
8  P.M.  The  map  shows  some  of  the  constellations  that  are  less  than  50  degrees 


103 


104  JUNIOR  SCIENCE 

If  you  look  at  an  almanac,  you  will  see  the  list  of  "  Signs 
of  the  Zodiac."  The  zodiac  is  made  up  of  the  twelve 
constellations  through  which  the  sun  seems  to  move ; 
they  were  used  by  the  ancients  to  tell  seasons. 

Why  does  the  sun  seem  to  make  a  journey  around 
the  sky  every  year?  The  answer  is  that  this  apparent 
moving  of  the  sun  is  due  to  the  revolution  of  the  earth 
around  the  sun  every  twelve  months.  So  we  must  get 
used  to  two  apparent  motions  in  the  sky,  both  of  them 
due  to  the  motions  of  the  earth  itself :  (1)  the  change 
from  sunrise  to  sunset  and  from  sunset  to  sunrise,  caused 
by  the  fact  that  we  are  being  carried  around  once  each 
day  by  the  rotation  of  the  earth ;  (2)  the  yearly  changes 
in  the  sky,  caused  by  the  fact  that  we  are  being  swept 
around  the  sun  and  back  to  the  place  of  starting,  in  one 
year.  You  have  all  had  the  strange  experience  of  imagin- 
ing that  the  train  on  which  you  were  riding  was  standing 
still,  while  barns,  trees,  and  people  were  dashing  madly 
by.  That  is  the  kind  of  experience  we  have  all  our  lives, 
unless  we  think  out  what  is  really  happening. 

Besides  the  sun  and  the  moon,  there  are  several  other 
heavenly  bodies  which  do  not  remain  in  any  constellation 
as  the  fixed  stars  do  ;  these  are  the  planets,  or  wandering 
stars.  They  appear  to  move  irregularly  among  the  stars 
because  they  really  revolve  about  the  sun,  just  as  our 
earth  revolves  around  it.  When  they  seem  to  be  in  a 
certain  constellation,  it  is  because  they  are  between  the 
earth  and  that  constellation. 

90.  What  is  the  Sun  Like? --The  sun  is  a  star. 
While  it  seems  to  us  to  be  very  large,  we  know  that  there 


THE  HEAVENLY  BODIES  105 

are  many  stars  larger  than  the  sun.,  Its  diameter  is 
about  864,000  miles,  or  about  109  times  the  diameter 
of  the  earth.  Its  volume  is  over  a  million  times  that  of 
the  earth.  As  we  see  it  in  the  sky,  it  seems  the  size  of  a 
full  moon,  but  this  is  because  it  is  much  farther  away  than 
the  moon.  The  heat  and  light  given  off  by  the  sun  are 
enormous,  but  our  earth  is  so  small  that  it  can  catch  only 
a  tiny  part  of  them.  Still  this  small  part  is  what  makes 
the  earth  fit  for  living  things,  instead  of  a  frozen  ball. 

It  has  been  calculated  that  if  the  sun  could  be  covered 
with  a  layer  of  ice  60  feet  thick,  the  heat  given  off  by  the 
sun  would  be  great  enough  to  melt  all  this  ice  in  one 
minute.  What  causes  the  sun's  heat  is  not  known,  but 
the  sun  is  not  a  burning  body,  as  a  piece  of  white-hot 
coal  is. 

If  we  use  a  smoked  glass,  we  can  look  at  the  sun's 
surface.  We  can  often  see  certain  irregular  spots  darker 
than  the  rest  of  the  surface.  These  are  called  sunspots. 
They  move  gradually  across  the  sun's  face  and  seem  to 
be  like  great  storms. 

The  sun  rotates  on  its  axis,  as  the  earth  does. 

91.  What  is  the  Solar  System  ?-- The  planets  are 
bodies  like  the  earth  in  that  they  revolve  about  the  sun 
and  shine  by  the  reflected  light  of  the  sun.  Many  of 
them  have  moons  that  revolve  about  them.  So  the  sun, 
the  planets,  and  the  moons  are  all  parts  of  the  solar  sys- 
tem. The  planets,  in  the  order  of  their  distance  from 
the  sun,  are :  Mercury,  Venus,  Earth,  Mars,  Jupiter, 
Saturn,  Uranus,  and  Neptune  (Fig.  58).  The  largest  of 
these  is  Jupiter,  with  a  diameter  nearly  11  times  that  of 


106 


JUNIOR  SCIENCE 


the  earth.     However,   all  the  planets  together  contain 
only  about  T^o  as  much  matter  as  the  sun. 


FIG.  58.  —  The  planets  revolve  about  the  sun.     The  average  distance  of  Nep- 
tune from  the  sun  is  about  2,700,000,000  miles.     What  is  that  of  the  earth? 

Mercury,  Uranus,  and  Neptune  cannot  be  seen  well 
without  a  telescope.     The  planets  are  always  found  in 


THE   HEAVENLY    BODIES  107 

the  same  belt  of  constellations  —  the  Zodiac  —  in  which 
we  see  the  sun  and  moon. 

The  time  needed  for  each  of  the  planets  to  revolve 
once  about  the  sun  is  as  follows : 

Mercury    ....  3    months  Jupiter 12  years 

Venus 1\  months  Saturn 30  years 

Earth 12    months  Uranus 84  years 

Mars 22    months  Neptune      ....  165  years 

While  the  earth's  rate  of  rotation  at  the  equator  is 
about  1000  'miles  an  hour,  its  rate  of  revolution  about 
the  sun  is  about  1000  miles  a  minute.  This  is  perhaps 
40  times  the  speed  of  a  bullet  as  it  leaves  the  muzzle  of 
an  army  rifle. 

92.  Our  Neighbor,  the  Moon.  —  After  we  have  thought 
of  the  enormous  distances  from  the  earth  to  the  sun  and 
the  stars,  the  moon  seems  just  across  the  way.  The 
moon  is  our  nearest  neighbor  in  the  heavens ;  its  average 
distance  is  about  240,000  miles.  The  moon's  diameter 
is  2163  miles  and  its  volume  is  about  TV  that  of  the  earth. 

Our  moon  revolves  in  a  path,  or  orbit,  that  is  nearly  a 
circle.  From  new  moon  to  new  moon  is  a  "  moon/'  or 
a  lunar  month;  it  is  about  29  days,  and  was  formerly  used 
in  reckoning  time.  The  surface  of  the  moon  (Fig.  59)  is 
made  up  of  what  seem  to  be  smooth  plains  and  also 
mountains  which  have  hollows,  or  craters,  that  make  them 
look  like  volcanoes. 

We  have  all  watched  the  change,  night  after  night, 
from  new  moon  to  full  moon.  Some  evening,  just  after 
sunset,  a  slender  crescent  is  seen  in  the  west.  This  is 


108 


JUNIOR  SCIENCE 


really  a  day  or  two  after  new  moon,  because  at  new  moon 
the  moon  is  too  near  the  sun  to  be  seen  at  all.  The  next 
evening  the  crescent  moon  is  thicker  and  farther  away 
from  the  sun.  This  continues  until  the  half  moon  is 
seen ;  the  moon  then  sets  about  6  hours  after  the  sun. 
The  period  from  new  moon  to  half  moon  is  called  the 

"& 


FIG.  59.  —  A  part  of  the  moon's  surface. 

"  first  quarter. "  From  new  moon  to  full  moon  the  moon 
is  said  to  be  "  waxing  "  or  growing.  The  full  moon 
rises  at  sunset ;  why  ?  From  half  moon  to  full  moon  is 
the  "  second  quarter.'7  After  full  moon  the  moon  is 
"  waning."  From  full  moon  to  half  moon  is  the  "  third 
quarter."  In  the  "  fourth  quarter  "  the  moon  shrinks 
once  more  to  a  crescent  (the  "  old  moon  ")  and  finally 


THE   HEAVENLY   BODIES 


109 


rises  just  before  the  sun.  But  the  moon  rises  about 
50  minutes  later,  on  the  average,  each  day  and  soon 
appears  again  as  a  crescent  just  after  sunset. 

Half  of  the  moon's  surface  is  always  lighted  by  the  sun, 
but  we  see  only  that  part  of  the  lighted  surface  which  is 
turned  toward  us. 
When  we  see  the  "  old 
moon  in  the  new 
moon's  arms/'  we  see 
the  "  old  moon  "  by 
earth  shine,  that  is, 
by  sunlight  that  is  first 
reflected  by  the  earth 
to  the  moon  and  then 
back  from  the  moon 
to  us. 

93.  What  are  Com- 
ets and  Meteors?- 
What  a  wonder  and  a 
terror  a  comet  (Fig. 
60)  must  have  been  to 
early  man !  Comets 
usually  appear  in  the 
heavens  unexpectedly, 
grow  brighter  night 
after  night,  move  among  the  constellations  until  they 
rise  and  set  with  the  sun,  then  move  away  from  the  sun, 
grow  smaller,  and  finally  disappear. 

Most  comets  are  small,  but  some  have  been  very  large 
and  beautiful.     Usually  they  can  be  seen  only  at  night, 


FIG.  60.  —  Naked-eye  view  >f  a  great  comet. 
(After  Young.) 


110  JUNIOR  SCIENCE 

but  the  very  bright  ones  are  also  visible  in  the  daytime. 
A  comet  has  the  appearance  of  a  shining  fog,  or  veil. 
It  is  rounded  off  at  one  end  into  a  blunt  "  head/'  while  a 
"  tail  "  of  light  is  spread  out  behind  it.  The  tail  always 
points  away  from  the  sun.  Stars  can  be  seen  shining 
right  through  the  material  of  a  comet.  The  comets  we 
see  all  revolve  about  the  sun,  but  in  paths  that  take  them 
far  out  of  our  vision  (see  Fig.  58)  for  many  years  at  a 
time. 

Meteors  are  heavenly  bodies  that  fall  on  or  into  the 
earth.  When  seen  at  night,  a  meteor  is  like  a  ball  of 
fire  followed  by  a  stream  of  light.  If  we  were  near 
enough,  we  could  hear  a  dull  roar  as  it  tears  its  way 
through  the  air.  Usually  it  throws  off  sparks  and  frag- 
ments of  matter  during  its  passage.  Sometimes  the 
meteor  disappears ;  sometimes  we  learn  where  it  strikes. 
Usually,  instead  of  falling  to  the  earth  a,s  one  body,  it 
bursts  into  many  pieces.  Often  tons  of  stones  come 
from  a  single  meteor.  A  few  meteors  consist  of  almost 
pure  iron  mixed  with  nickel. 

Did  you  ever  see  a  shooting  star  ?  Shooting  stars  are 
small  fragments  of  matter  that  fall  into  the  earth 's  at- 
mosphere. They  are  very  numerous  and  many  may  be 
seen  on  a  clear  night.  They  never  reach  the  ground, 
except  in  the  form  of  dust  and  ashes  so  fine  that  we 
cannot  see  them  falling.  Did  you  ever  realize  before 
that  matter  comes  to  us  all  the  time  from  the  space 
through  which  the  earth  moves  ? 

94.  Exercises. —  1.  Have  you  read  about  "daylight  saving "? 
Why  was  it  carried  out?  How? 


THE   HEAVENLY  BODIES  111 

2.  Why  is  a  day  divided  into  "  forenoon  "  and  "  afternoon  " 
ID  stead  of  day  and  night? 

3.  The  Indian  said  that  an  event  was  so  many  "  moons  "  ago; 
what  did  he  mean? 

4.  What  festival  is  still  fixed  by  lunar,  or  moon,  time? 

5.  Name  the  planets  hi  the  order  of  their  distance  from  the  sun. 

6.  Coat  a  piece  of  glass  with  soot  and  see  if  you  can  find  "  sun- 
spots  "  on  the  sun. 

7.  Does  the  moon  revolve  about  the  sun? 

8.  What  causes  the  four  "  quarters  "  of  the  moon? 

9.  What  is  the  horizon?     The  zenith?     The  zodiac? 

10.  When  is  wheat  harvested  in  Iowa?     In  Argent ina? 

11.  What  do  you  suppose  causes  a  "  ring  around  the  moon  "?    Is 
the  ring  near  the  moon? 

12.  How  do  you  imagine  the  earth  would  look  if  seen  from  the 
moon? 

13.  What  daily  path  would  a  star  have  if  you  were  at  the  earth's 
north  pole  ?     What  path  would  the  sun  have  ? 

14.  On  a  sunny  day  measure  the  length  of  the  shadow  of  a  certain 
post,  such  as  a  fence  post,  in  the  morning,  at  noon,  and  in  the  late 
afternoon.     When  is  it  the  shortest?     Why? 

Measure  the  shadow  at  noon  every  week  or  two  for  several  months 
and  keep  an  accurate  record  of  the  month  and  day  on  which  the  meas- 
urement was  taken.  What  change  do  you  notice?  Explain  it.  On 
what  date  would  the  noonday  shadow  be  the  longest?  Why? 

15.  In  an  almanac  read  the  time  of  sunrise  and  sunset  from  autumn 
to  spring.     What  day  is  shortest?     In  what  month  does  the  sun  rise 
at  almost  the  same  hour  and  minute  for  several  days  in  succession  ? 
Is  this  true  at  any  other  season  ? 


CHAPTER  XII 
FORCE  AND  ENERGY 

95.  What  Holds  the  Solar  System  Together  ?  — Have 
you  been  asking  yourself,  as  you  have  studied  about 
the  solar  system,  why  the  planets  in  their  great  orbits 
swing  around  the  sun  year  after  year,  and  what  it  is  that 
holds  the  sun  and  all  its  planets  together?  Before  we 
answer  this  question,  let  us  think  of  simpler  questions. 
In  the  first  place,  why  does  a  body  that  is  not  held  up, 
or  supported  in  some  way,  fall  to  the  earth?  Why  is  it 
that  a  bullet  shot  upward  from  a  rifle  does  not  continue 
in  its  flight  off  into  space,  but  always  returns  to  the 
earth?  Sir  Isaac  Newton  gave  the  reason  when  he 
said  that  the  earth  pulls  objects  toward  itself,  or  attracts 
other  objects.  Do  you  suppose  so  small  an  object  as  an 
apple  hanging  on  a  tree  attracts  the  earth  ?  Why  not  ? 
In  proportion  to  its  weight  it  pulls  the  earth  as  much  as 
the  earth  pulls  it. 

Does  it  seem  impossible  that  an  orange  lying  on  a 
table  attracts,  or  draws  toward  it,  another  orange,  lying 
beside  it  ?  It  is  not  easy  to  show  this,  because  the  earth 
pulls  both  oranges  strongly  toward  itself ;  but  by  means 
of  a  celebrated  experiment  it  was  shown  clearly  that  one 
body  of  matter  attracts  another  near  it.  A  large  ball  of 
lead  (Fig.  61)  and  a  small  one  of  copper  were  hung  side 
by  side,  and  it  was  possible  to  see  distinctly  that  the  copper 

112 


FORCE  AND  ENERGY 


113 


ball  moved  over  toward  the  lead  ball.  So  we  know 
that  this  pull  which  the  earth  has  for  bodies  near  it,  is 
also  present  between  two  bodies  on  the 
earth.  We  call  this  earth  pull,  gravity. 
Scientists  believe  that  the  same  pull  that 
the  earth  has  for  objects  near  it  also  exists 
between  the  sun,  the  earth,  and  other  planets. 
When  we  speak  of  this  pull  between  the 
bodies  of  the  solar  system,  we  call  it  gravi- 
tation. Therefore,  it  is  gravitation  which 
holds  the  solar  system  together. 

96.  Why  Does  a  Body  Have  Weight?  - 
Do  you  know  of  any  object 
that  is  without  weight? 
We  learned  that  gases,  such 
as  air,  have  weight,  as  well 
as  do  solids  and  liquids  (cf. 
§  10) .  How  do  we  weigh  an 
object?  If  we  use  a  spring  balance  (Fig. 
62),  we  find  that  the  balance  consists  of 
a  spring  which  can  be  uncoiled  or  stretched 
by  the  object.  When  the  object  pulls 
the  spring  so  far  that  the  pointer  is  at 
the  mark  for  3  pounds,  the  object  weighs 
3  pounds.  But  why  does  the  object 
stretch  the  spring  at  all?  The  answer 
is  that  the  earth  pulls  the  matter  of  the 
object  toward  itself  with  such  a  force  that 
the  spring  is  stretched  to  the  3-pound  mark.  So  it  is 
gravity,  or  the  earth  pull,  that  causes  a  body  to  have 


FIG.  61.  — 
There  is  a  pull,  or 
attraction,  be- 
tween two  por- 
tions of  matter. 


FIG.  62.  —  The 
spring  is  stretched 
by  the  earth's  pull 
upon  the  object 
weighed. 


114 


JUNIOR  SCIENCE 


I 


FIG.  63.  —  Leaning  Tower  of  Pisa. 


weight.  Does  it  make 
any  difference,  so  far  as 
the  earth  is  concerned, 
whether  the  object  weigh- 
ing 3  pounds  is  feathers, 
or  water,  or  lead?  Of 
course  not,  for  the  earth 
has  the  same  pull  upon 
all  objects  that  contain 
equal  quantities  of  mat- 
ter, of  whatever  sort  the 
matter  may  be. 
97.  In  What 
Direction  Does 
the  Earth  Pull? 

If  you  drop  a  stone  from  your  hand,  in  what 
direction  does  it  fall  ?  It  falls  "  straight  down/' 
or  vertically ,  because  gravity  acts  in  that  direc- 
tion. Bricklayers,  masons,  and  carpenters  use  a 
string  with  a  weight  attached  (a  plumb  line)  to 
guide  their  work,  so  that  their  walls  shall  be 
"  plumb/7  or  vertical.  In  doing  this  they  de- 
pend upon  gravity  to  pull  "  straight  down  " 
and  to  give  them  a  reliable  line. 

Before  the  time  of  Galileo  there  was  a  belief  that  heavy 
materials,  such  as  metals,  fall  more  rapidly  than  light 
materials,  such  as  papers  or  feathers.  Galileo  let  objects 
of  different  materials  fall  from  the  leaning  tower  of  Pisa 
(Fig.  63),  and  decided  that  the  earth  pull  gives  the  same  at 
speed  to  all  falling  bodies,  but  that  the  air  interferes  with  rate. 


FORCE  AND  ENERGY 


115 


the  lighter  ones.  When  air  pumps  were  made,  so  that  a  long  glass 
tube  could  be  freed  from  air  (Fig.  64),  it  was  found  that  a  feather  falls 
just  as  rapidly  as  a  coin  or  a  bullet. 

98.  What  is  the  Density  of  Water  ?  —  Which  is  lighter, 
wood  or  lead?  In  saying  that  wood  is  lighter  than  lead, 
we  do  not  mean  that  a  large  board  is  lighter  than  a  small 
piece  of  lead,  but  we  mean  that  if  we  have  a  block  of  wood 
of  the  same  size,  or  volume,  as  the  lead,  the  wood  is  lighter 
than  lead.  We  express  this  fact  by  saying  that  the 
density  of  the  wood  is  less  than  that  of  the  lead  (Fig.  65). 


Gold 


Lead 


Copper 


Coal 


Wood 


FIG.  65.  —  Cubes  containing  equal    weights  of    these    materials    have    very 
different  volumes.     Which  is  the  more  dense,  lead  or  copper? 

In  the  same  way  we  say  that  the  density  of  water  is  less 
than  that  of  lead  or  iron,  but  greater  than  that  of  kerosene 
or  air. 

We  express  the  density  of  a  solid  or  liquid  by  com- 
paring its  density  with  that  of  water  (Table  III,  Ap- 
pendix). Thus,  when  we  say  that  marble  has  a  density 
of  2.7,  we  mean  that  it  is  2.7  times  as  heavy  as  water. 

99.  Why  Does  a  Body  Float?  —  If  you  are  asked  why 
a  cork  or  a  pine  board  floats  on  water,  you  answer  that 
it  is  lighter  than  water,  or  has  a  smaller  density  than 
water.  Does  any  body  float  wholly  on  the  surface, 


116 


JUNIOR  SCIENCE 


S&     Frl 


without  pushing  some  of  the  water  out  of  the  way?  Of 
course  not ;  the  heavier  it  is,  so  long  as  it  floats  at  all, 
the  deeper  it  will  sink  into  the  water.  A  piece  of  cork 
with  a  density  of  £  will  sink  until  \  of  its  volume  is  below 
water ;  a  piece  of  pine  wood  with  a  density  of  ^  will  sink 
halfway.  A  cake  of  ice  having  a  density  of  about  0.92 
will  sink  until  0.92  of  its  volume  is  below  water.  Thus 
less  than  tV  of  an  iceberg  is  above  water. 

Did  you  ever  think  that  it  is 
gravity  that  makes  bodies  sink  or 
float  ?  If  you  push  a  pine  block 
down  to  the  bottom  of  a  pail  of 
water,  it  bobs  up  again,  because* 
gravity  pulls  the  heavier  sub- 
stance (the  water)  as  near  as 
possible  to  the  earth.  The  water 
then  pushes  up  the  wood.  For 
the  same  reason,  when  we  say 
that  a  column  of  warm  air  ascends, 
we  mean  that  gravity  pulls  down 
on  the  heavy,  cold  air,  and  this  heavier  air  pushes  the 
warm  air  up.  This  is  the  way  that  gravity  causes  the 
winds  (cf.  §79). 

Have  you  ever  tried  to  lift  a  heavy  stone  up  from  the  bottom  of  a 
stream  or  pond?  If  you  have,  you  must  have  been  surprised  to  find 
that  the  stone  seemed  to  get  heavier  when  it  left  the  water.  In  the 
case  of  a  floating  board  the  water  supports  all  of  the  weight.  In  the 
case  of  the  stone  the  water  supports  part  of  its  weight.  We  have  to 
make  a  greater  effort  when  we  lift  the  stone  entirely  out  of  the  water, 
for  the  water  then  ceases  to  push  up,  or  buoy  up,  the  stone.  For  this 
reason  any  object  weighs  less  in  water  than  in  air  (Fig.  66). 


FIG.  66.  —  An  object  weighs 
.  less  in  water  than  in  air,  be- 
cause it  is  buoyed  up  by  the 
water. 


FORCE  AND  ENERGY 


117 


FIG.  67. —  The  pencil  and 
knives  take  such  a  position 
that  the  center  of  gravity  is 
below  the  point  of  support. 


100.  Can  You  Stand  an  Egg  on  End  ?  —  Why  does  an 
egg  or  a  top  prefer  to  lie  on  its  side?  Why  is  it  so  hard 
to  make  a  slender  stick  stand  upright?  Everywhere  we 
find  examples  of  the  fact  that 
irregular  bodies  must  be  placed 
in  certain  positions,  or  they  will 
turn  over.  You  have  seen  tops 
that  stood  upright  while  spinning. 
A  pencil  may  be  made  to  stand  on 
its  point  if  weights,  such  as  knives, 
are  attached  to  it,  as  in  Fig.  67. 
An  empty  ship  must  be  ballasted, 
or  it  is  in  danger  of  "  turning 
turtle. "  So  men  know  well  that  if  they  want  to  keep  a 
body  upright,  they  must  see  to  it  that  the  matter  of  the 
body  is  properly  distributed.  To  understand  how  the 
matter  of  a  body  must  be  distributed  in  order  that  the 

body  may  stand,  let  us  use 
the  following  illustrations.  If 
a  wooden  ball  is  placed  on  a 
smooth,  horizontal  surface,  it 
will  lie  in  any  position,  be- 
cause all  the  matter  in  the 
ball  is  evenly  distributed  about 
its  center,  but  if  a  ball  is  half 
wood  and  half  lead,  more  of 
the  matter  is  in  the  lead  half 

of  the  ball  than  in  the  wood  half,  so  that  the  ball  turns 
until  the  lead  is  below.  You  have  all  played  with  the 
toy  "  tumbler  "  that  will  not  lie  on  its  side ;  this  toy  has 


FIG.  68.  —  The  lower  part  of 
the  toy  is  of  heavy  material,  while 
the  upper  part  is  of  light  material ; 
so  the  toy  cannot  be  made  to  lie  on 
its  side. 


118  JUNIOR  SCIENCE 

heavy  material  in  its  lower  part  and  lighter  material  in 
the  upper  part  (Fig.  68) . 

We  speak  of  the  point  about  which  all  the  matter  of 
a  body  is  balanced  as  the  "  center  of  gravity /'  or  "  center 
of  mass/'  of  the  body.  A  body  is  able  to  stand  when 
we  can  keep  the  center  of  gravity  above  the  base  on 
which  the  body  rests.  But  a  body  stands  best,  or  is 
"  most  stable/'  when  this  center  is  in  the  lowest  position 
possible.  If  a  body  is  free  to  move,  it  will  turn  until 
this  center  is  in  its  lowest  position. 

Why,  then,  does  an  egg  lie  on  its  side?  Because  in 
this  position  the  center  of  gravity  of  the  egg  is  lowest. 
The  egg  is  so  rounded  that  we  cannot  support  it  and 
keep  its  center  of  gravity  above  the  spot  where  the  egg 
touches  the  table.  If  we  make  a  dent  in  the  end  of  the 
egg,  of  course  we  can  make  it  stand  upright.  We  our- 
selves can  stand  only  when  we  keep  the  center  of  gravity 
of  our  bodies  directly  above  our  feet. 

101.  Can  a  Body  Move  Itself?  —  What  happens  when 
you  are  standing  in  a  street  car  and  the  car  suddenly 
stops  ?  Your  feet  stop  with  the  car,  but  your  body  goes 
on  and  you  fall.  What  happens  when  the  car  starts 
suddenly?  When  a  car  turns  a  corner,  your  body  travels 
straight  ahead,  while  your  feet  follow  the  car.  So  you 
fall  to  one  side.  When  you  play  "  tag  "  and  your  play- 
mate comes  rushing  toward  you  at  full  speed,  why  do 
you  spring  aside,  or  "  dodge  "?  Is  it  not  because  you 
know  that  he  cannot  stop  himself  at  once?  What  is 
true  of  our  bodies  is  true  of  every  body  of  matter.  Does 
a  baseball  start  itself?  No,  it  must  be  thrown.  Does 


FORCE  AND  ENERGY  119 

it  stop  itself?  No,  it  stops  because  it  rubs  against  the 
uneven  places  on  the  ground,  or  because  the  air  resists 
its  passage,  or  because  some  one  catches  it.  Bodies  of 
matter  are  helpless,  they  cannot  move  themselves,  or 
set  themselves  in  motion,  or  stop  themselves,  or  move 
in  any  direction  except  in  a  straight  line,  unless  something 
acts  upon  them.  We  call  this  quality  of  matter  inertia. 
So  matter,  besides  taking  up  space  and  having  weight, 
has  inertia. 

You  can  think  of  ever  so  many  cases  in  which  we  make  use  of  the 
inertia  of  matter;  some  have  already  been  given.  When  you  shake 
the  dirt  out  of  a  rug,  you  really  shake  the  rug  away  from  the  dirt ; 
the  dirt  remains  behind.  Air  has  inertia,  just  as  it  occupies  space  and 
has  weight.  Just  try  to  push  the  air  away  suddenly  with  a  large  fan 
or  a  hoop  covered  with  a  newspaper ;  or  try  to  shut  a  door  against  a 
strong  wind,  and  you  will  find  that  the  air,  too,  is  hard  to  stop  and 
to  start. 

102.  Why  Does  a  Pendulum  Swing?  —  Make  a  pen- 
dulum by  hanging  a  weight,  such  as  a  piece  of  lead  or  iron, 
by  means  of  a  long  thread  from  a  gas  jet  or  other  support. 
Draw  the  weight  aside  and  let  go  of  it.  What  happens  ? 

Did  you  lift  the  weight  when  you  drew  it  aside  ?  Prove 
this  by  measuring  the  distance  to  the  floor  for  both 
positions  of  the  weight.  Does  the  pendulum  fall  when 
you  let  go  of  it?  What  makes  it  swing?  Why  does  it 
not  stop  at  the  lowest  point  of  its  path?  Is  a  swing  a 
pendulum?  What  stops  the  swing  when  we  "  let  the 
old  cat  die  "? 

Make  a  pendulum  with  a  thread  about  39  inches  long  and  count 
the  number  of  swings  it  makes  in  a  minute.  Adjust  the  length  of 


120  JUNIOR  SCIENCE 

the  thread  so  that  the  pendulum  will  make  60  swings  a  minute,  or 
one  a  second.     How  long  is  the  pendulum? 

Try  to  make  a  pendulum  that  will  swing  120  times  a  minute,  or 
twice  a  second;  how  long  is  it?  Make  one  with  a  thread  about  13 
feet  long  and  find  a  support  for  it.  Count  the  number  of  swings  it 
makes  in  a  minute. 

103.  What  is  a  Force  ?  -  -  Think  why  it  is  that  a  base- 
ball begins  to  move.  Is  it  not  because  some  other  body 
-  the  pitcher,  perhaps  —  gives  motion  to  it,  or  "  throws 
it  "?  Why  does  a  bullet  move?  Is  it  not  the  exploding 
powder  that  causes  the  motion?  Why  does  the  cork  of 
a  popgun  fly  out?  It  is  the  air  we  have  compressed  in 
the  "  gun  "  that  pushes  out  the  cork.  In  the  "  bow  and 
arrow,"  on  the  other  hand,  the  bent  bow  straightens 
itself  and  so  sends  the  arrow  to  its  mark. 

What  shall  we  call  a  body  of  matter  that  gives  motion 
to  another  body,  or  stops  its  motion,  or  changes  the 
direction  of  its  motion?  We  call  it  a  force,  or,  better, 
we  say  that  it  exerts  force  upon  the  other  body  of  matter. 
A  force  is  a  push  or  a  pull.  So  the  earth  exerts  force 
upon  the  moon  and  other  bodies  near  it ;  we  call  this 
the  force  of  gravitation.  When  a  pitcher  throws  a  ball, 
or  a  horse  pulls  a  wagon,  the  muscular  force  of  the  pitcher 
or  the  horse  is  causing  motion.  Air  exerts  force  both 
by  pushing  against  bodies  that  pass  through  it,  and  also 
as  wind,  which  is  air  in  motion.  The  force  of  the  air 
at  rest  makes  it  possible  for  a  moving  airplane  to  "  fly  " 
and  a  balloon  to  go  up ;  while  the  force  of  air  in 
motion  makes  kites  rise,  windmills  turn,  and  ships  sail 
the  sea. 


FORCE  AND  ENERGY  121 

The  resistance  which  a  body  meets  when  it  pushes  its 
way  through  air  or  water,  or  along  the  ground,  and  which 
one  part  of  machinery  meets  as  it  rubs  against  another 
part,  is  a  very  important  force ;  we  call  it  friction.  How 
do  men  make  the  friction  between  a  wheel  and  its  axle 
as  small  as  possible  ? 

104.  When  Has  a  Body  Energy?  —  What  do  we  mean 
when  we  say  that  one  person  has  energy  and  another 
has  not?     In  a  general  way,  we  mean  that  one  person 
can  do  work  and  another  cannot.     This  is  what  energy 
means  in  science,  too:  the  ability  to  do  work.     When  we 
lift  a  hammer,  we  do  work  upon  that  hammer.     Because 
we  lift  it  against  gravity  and  thus  do  work  upon  it,  it  in 
turn  can  do  work  when  gravity  pulls  it  down :    it  helps 
us  to  break  a  nutshell,  or  drive  a  nail.     Why  is  it  so  much 
harder  to  drive  a  nail  into  the  ceiling  than  into  the  floor  ? 

We  can  think  of  energy  in  two  forms :  energy  of  posi- 
tion and  energy  of  motion.  The  hammer  or  pendulum, 
while  it  is  held  up  in  the  air,  has  energy  of  position ; 
when  it  falls,  its  energy  is  changed  into  energy  of  motion. 
The  water  of  a  waterfall  has  energy  of  position  at  the  top 
of  the  fall,  but  it  has  energy  of  motion  as  it  comes  down. 
What  kind  of  energy  is  in  a  wound-up  clock  spring  ? 

105.  Why  Do  Objects  Fly  from  the  Center  ?  —  Have 
you  ever  watched  the  mud  fly  off  a  carriage  wheel,   or 
the  water  fly  off  a  revolving,  grindstone?     If  you  have, 
you  must  have  noticed  that  the  mud  or  the  water  flies 
from  the  revolving  wheel  or  stone  in  a  straight  line.     Why 
is  it  that  while  the  mud  is  attached  to  the  wheel  it  re- 
volves in  a  circle  with  the  wheel,  yet  the  instant  it  is 


122 


JUNIOR  SCIENCE 


free  from  the  wheel  it  flies  off  in  a  straight  line?  We 
notice,  too,  that  the  lines  along  which  the  mud  flies  off 
do  not  come  straight  out  from  the  center  of  the  circle, 
but  just  touch  the  outside  of  the  circle  (Fig.  69,  a) ;  such 
lines  are  called  tangent  (tan'jent)  lines.  The  reason  for 
this  "  flying  off  from  the  center  '•'  is  the  same  as  the  one 

that  explains  why 
you  lurch  side- 
ways when  a  car 
moves  around  a 
curve :  the  inertia 
of  matter  keeps 
the  mud  moving 
in  the  same  direc- 
tion in  which  it 
was  going  at  the 
moment  it  left  the 
wheel. 

Attach  a  small 
rubber  ball  to  a 
string  and  whirl 
it  carefully  about 
your  hand.  Its  path  is  a  circle;  but  if  you  let  go  of 
the  string,  the  ball  flies  off  in  a  tangent  line.  The 
circular  path  is  caused  by  the  resistance  of  the  string, 
which  makes  the  ball  remain  always  at  the  same  distance 
from  your  hand,  and  by  the  inertia  of  the  ball,  which, 
if  it  could,  would  make  the  ball  fly  off  in  a  tangent  line. 

This  pull  which  matter  exerts  in  its  effort  to  fly  off  a 
revolving  body,  is  called  the  centrifugal  force  of  the  body. 


FIG.  69.  —  a.  The  ball  moves  in  a  circle  because 
inertia  tries  to  take  it  forward  in  a  straight  line, 
while  the  string  holds  it  always  at  the  same  distance 
from  the  center,  b.  As  the  pail  is  whirled  by  the 
untwisting  of  the  rope,  the  water  is  piled  up  against 
the  sides  of  the  pail.  Why? 


FORCE  AND  ENERGY 


123 


It  is,  of  course,  a  result  of  the  inertia  of  the  matter  in 
the   body.     Do   you   suppose   men   can   use   centrifugal 
force  for  anything?     Study  a  whirling  pail  (Fig.  69,  6) 
and  a  dairy  separator 
(Fig.  70). 

106.  Why  Do  Plan- 
ets   Revolve   around 
the  Sun?— The  plan- 
ets are  much   larger 
than  the  ball  that  we 
whirled  with  a  string, 
but   the  reason  why 
their  path,   or  orbit, 
is  round  is  much  the 
same.      Instead  of  a 
string   we    have    the 
force  of  gravity.     If 
this  acted  alone    the 
planets  would  fall  into 
the  sun.      If  gravity 
were    to    stop,    they 
would  go  off  in  straight 
lines  into  space     And 
so  the  two  forces  :  the 
tendency    of    matter 

to  move  off  in  tangent  lines,  together  with  gravitation, 
makes  the  planets  revolve  about  the  sun,  just  as  the 
ball  we  whirl  revolves  about  our  hand. 

107.  Is  There  Any  Force  in  a  Water  Surface  ?  —  Have 
you  ever  thought  why  a  piece  of  clean  glass  becomes  wet 


(Copyright  by  Mclntosh  Stercopticon  Co.) 
FIG.  70.  —  In  the  dairy  separator  use  is 
made  of  "centrifugal  force."  During  the 
whirling,  the  skim  milk,  which  is  heavier  than 
the  cream,  moves  out  farther  than  the  cream  ; 
thus  the  two  are  separated.  What  was  the  old 
way  of  removing  the  cream  ? 


124 


JUNIOR   SCIENCE 


FIG.  71.  —  Force  must  be 
exerted  to  tear  the  glass  away 
from  the  water. 


when  put  into  water,  while  a  piece  of  greasy  glass  does 
not?  If  we  hold  a  sheet  of  glass  down  against  a  water 
surface,  and  then  try  to  pull  the  glass  away,  we  find  that 

we  must  exert  more  force  than  is 
needed  to  lift  the  glass  against 
gravity  alone  (Fig.  71).  Another 
force  resists  our  tearing  the  glass 
away.  The  force  that  holds  the 
water  particles  together  is  called 
cohesion,  while  the  force  that 
holds  two  different  substances,  as 
water  and  glass,  together  is  called 
adhesion.  A  postage  stamp  ad- 
heres to  the  envelope.  The  ad- 
hesion of  water  to  glass  is  a  greater  force  than  the  cohesion 
of  water,  or  the  water  would  not  wet  the  glass. 

Have  you  ever  thought  why  liquids  form  drops?  We  know  that 
a  large  surface  of  water  is  flat  (horizontal),  because  gravity  pulls  down 
on  all  parts  of  the  surface.  But  when  the  body  of  water  is  small 

(a  drop),  the  effect  of  gravity     

is  also  small,  and  cohesion  is 

able  to  pull  the  water  into  the 

form  of  a  sphere.     The  water 

surface    acts    like    a    tightly 

stretched,  elastic  covering,  say 

of  rubber.    That  there  is  such 

an  elastic  surface  is  shown  by  the  trick  by  which  we  can  float  a  needle 

upon  water  (Fig.  72).    We  grease  the  needle  slightly,  so  that  water 

will  not  wet  it,  and  then  .put  it  down  carefully  on  the  water's  surface. 

A  fork  will  help  us  to  do  this.     Note  how  the  needle  stretches  the 

elastic  water  surface,  without  breaking  it.     Is  the  needle  heavier,  or 

lighter,  than  water? 


FIG.  72.  —  The  greased    needle  stretches 
the  water  surface  without  breaking  it. 


FORCE   AND  ENERGY 


125 


108.  Why  Does  a  Blotter  Absorb  Ink?  — Did  you 
ever  wonder  why,  if  you  touch  a  drop  of  ink  with  a 
blotter,  the  whole  drop  flows  into  the  blotter?  Or  have 
you  ever  left  one  corner  of  a  dry  towel  in  a  dish  of  water 
and  found  the  water  rose  into  the  towel?  The  force 
exerted  is  called  capillary  action.  Capillary  means 
hairlike.  The  action  is  so  called  because  it 
takes  place  best  in  tiny  tubes. 

Capillary  action  takes  place  between  water 
and  glass  tubes  because  the  water  wets  the 
inside  of  the  tube  and 
because  the  surface  of 
the  water  is  elastic. 
If  we  have  some  water 
in  a  dish,  or  in  a  large 
tube,  the  water  is 
raised  only  at  its  edge 
(Fig.  73).  The  elastic 
surface  does  not  have 
force  enough  to  lift 
the  water  in  a  column. 


FIG.  73.  —  The  elastic  water  surface  has 
force  enough  to  lift  the  water,  against  gravity, 
up  into  the  tube  and  around  the  side  of  the  dish. 


But  if  we  use  a  tiny  tube  —  a  capillary  tube  —  the 
weight  of  water  is  small  and  the  force  of  the  elastic 
surface  pulls  the  column  of  water  up  in  the  tube.  In 
blotters,  cloth,  string,  soil,  and  other  loose  materials, 
the  spaces  are  so  small  that  they  act  as  a  multitude  of 
fine  tubes. 

In  watering  a  potted  plant  we  often  set  the  pot 
in  a  dish  of  water ;  how  does  the  water  get  up  to  the 
plant  ? 


126  JUNIOR  SCIENCE 

109.  Exercises. —  1.   What  do  we  call  the  force  which  you  must 
overcome  in  driving  a  nail  into  wood  ? 

2.  What  causes  water,  mercury,  kerosene,  and  other  liquids  to 
form  drops?     Why  does  a  drop  of  water  not  remain  spherical  on  a 
table  while  a  drop  of  mercury  does? 

3.  Why  is  it  possible  to  ride  on  a  bicycle  and  not  fall  to  one  side 
or  the  other? 

4.  Why  does  a  steel  ship  float  ? 

5.  Why  does  an  engine  begin  to  slow  up  long  before  it  is  near  the 
station? 

6.  How  could  you  find  out  which  is  the  heavier,  gasoline  or  water ; 
olive  oil  or  water ;  marble  or  gold ;  iron  or  lead ;  salt  brine  or  water  ? 

7.  If  dropped  from  the  same  height  at  the  same  time,  which  will 
strike  the  ground  the  sooner,  a  pound  bag  of  feathers  or  a  pound  bag 
of  iron  nails  ? 

8.  Why  is  it  hard  for  a  two-legged  chair  to  stand?    Which  is 
harder  to  push  over,  a  three-legged  or  a  four-legged  stool?     Has  a 
three-legged  stool  any  advantage  over  a  four-legged  one  on  rough 
ground? 

9.  When  you  pitch  a  baseball,  or  bat  a  tennis  ball,  why  do  you 
have  to  "  allow  for  the  wind  "?    Does  an  apple  fall  straight  down  on 
a  windy  day?    Why?    Does  this  mean  that  gravity  is  not  pulling 
straight  down  on  such  a  day? 

10.  Why  should  a  brick  or  stone  wall  be  built  "  plumb  "  ?    Why 
does  not  the  "  leaning  tower  "  fall  over? 

11.  Would  it  be  easier  for  you  to  float  in  fresh  water  or  salt  water? 
Why? 

12.  Would   iron  float   on   mercury?     See  Appendix,   Table    III, 
About  how  much  of  the  iron  would  sink  into  the  mercury? 


CHAPTER  XIII 
SUBSTANCES 

110.  What    is    a    Substance  ?  — Substances    are    the 
different  kinds  of  matter;  have  you  ever  thought  what 
a  wonderful  variety  of  them  there  is  in  this  world  of 
ours  ?   Some  of  them  are  gases,  some  are  liquids  and  some 
are  solids.     Some  are  colorless,  some  have  color  ;  some  dis- 
solve, others  do  not ;  some  are  light  and  some  are  heavy ; 
some  we  can  see  through   (they  are  transparent)   and 
others  we  cannot  see  through  (they  are  opaque) ;  some 
we  can  set  on  fire  and  others  refuse  to  burn.     Then,  too, 
some  substances,  as  limestone,  air,  and  water,  are  very 
abundant  in  the  earth,  while  others,  like  gold  and  dia- 
monds,   are    rare.     Thousands    of    different    substances 
are  known  and  many  more  will  probably  be  discovered 
as  time  goes  on.     The  qualities  by  which  we  tell  sub- 
stances from  one  another  are*  called  the  properties  of 
those  substances.     Thus,  one  of  the  properties  of  salt 
and  sugar  is  their  taste ;  the  color,  odor,  and  density  of 
a  substance,  whether  it  will  dissolve  or  burn,  and  many 
other  qualities  are  also  properties  of  the  substance. 

Tell  all  the  properties  you  know  of  pine  wood,  soap, 
sugar,  glass,  iron,  and  milk. 

111.  Can  Substances  Be  Changed?  — It  is  easy  for 
us  to  see  that  many   substances  change,  for  they  gain 
new  properties  or  lose  old  ones.     Liquid  water  becomes 

127 


128  JUNIOR  SCIENCE 

a  gas  (water  vapor)  or  a  solid  (ice).  A  "  tin  "  can  rusts 
away.  Fruit  juices  ferment ;  milk  sours ;  cut  grass  be- 
comes hay.  If  we  examine  a  cliff,  we  see  heaps  of  chips 
and  dust  at  its  base ;  these  were  broken  off  from  the  cliff. 
Wonderful  changes  take  place  in  our  own  bodies.  Men 
eat  many  different  kinds  of  food,  but  in  some  way  these 
foods  are  changed  into  the  material  of  which  man's  body 
is  built  up. 

If  we  put  iron  into  a  fire,  it  becomes  hot.  It  may 
become  red  or  white-hot  and  give  off  light.  But  if  it  is 
removed  from  the  fire,  it  gradually  gives  off  the  heat  it 
gained  and  finally  looks  just  as  at  first.  Men  may  break 
off  coal  in  a  mine  hoist  it  above  the  surface,  and  haul  it 
to  our  coal  bin,  but  it  is  still  coal.  These  changes  have 
not  really  altered  the  coal.  We  call  such  changes  physical 
changes.  But  if  the  iron  poker  is  left  in  a  damp  cellar, 
it  rusts  (cf.  §  34).  If  we  burn  the  coal,  its  carbon  disap- 
pears and  carbon  dioxide  is  formed.  The  iron  of  the  poker 
and  the  carbon  of  the  coal  have  each  combined  with 
oxygen  to  form  new  substances  :  rust  and  carbon  dioxide. 
Such  changes  as  these  are  called  chemical  changes,  be- 
cause they  are  studied  in  chemistry. 

112.  Can  Water  Be  Changed?  —  Of  course  we  know 
that  water  can  be  changed  to  a  gas  or  a  solid  and  then 
changed  back  into  liquid  water.  But  can  it  be  broken 
up  into  other  substances  ?  If  you  can  get  the  apparatus, 
the  following  experiment  (Fig.  74)  will  give  you  the 
answer : 

Let  two  wires  from  a  battery  of  several  cells,  or  some 
other  source  of  the  electric  current,  pass  into  a  vessel 


SUBSTANCES 


129 


Oxygen  t| 


containing  water  and  a  very  little  sulphuric  acid.  The 
wires  inside  the  vessel  are  of  platinum  and  they  have 
tips  of  platinum  foil  so  as  to  make  their  surfaces  larger. 
We  call  the  ends  of  the  wires  the  poles  of  the  battery. 
If  we  were  to  put  the  platinum  poles  together,  the  current 
would  have  a  complete  passageway,  or  circuit,  without 
going  through  the  dilute  acid.  But  if  we  keep  the  poles 
apart,  the  current  must  pass  through  the  dilute  acid. 
While  the  acid  is  carrying  the 
current  from  one  pole  to  another, 
a  strange  thing  happens :  bub- 
bles of  gas  arise  from  each  pole. 
We  can  collect  the  gas  by  putting 
over  each  pole  a  test  tube  filled 
with  some  of  the  dilute  acid. 
We  then  see  that  one  tube  be- 
comes filled  with  the  bubbles 
about  twice  as  rapidly  as  the 
other.  If  we  put  a  burning  splinter  into  the  gas  that 
is  collected  the  more  slowly,  the  splinter  burns  more 
brightly  than  in  air.  If  the  splinter  is  merely  glow- 
ing, it  will  burst  into  flame.  The  gas  in  this  tube  is 
oxygen.  If  we  bring  a  flame  near  the  other  gas,  the  gas 
takes  fire  with  a  slight  explosion,  or  "  pop/'  and  then 
burns  with  a  blue  flame  that  is  almost  invisible.  This 
gas  is  called  hydrogen,  meaning  "  water-former. "  The 
hydrogen  and  oxygen  are  obtained  by  the  breaking  up 
of  water  by  the  electric  current ;  we  call  the  experiment 
the  electrolysis  (e-lek-trol'i-sis)  of  water.  Is  it  a  physical 
change,  or  a  chemical  one? 


FIG.  74.  —  The  electric  cur- 
rent breaks  up  the  water  (it  is 
really  very  dilute  sulphuric 
acid)  into  hydrogen  and  oxygen. 


130  JUNIOR  SCIENCE 

113.  What   is   an   Element  ?-- The   breaking   up   of 
water  by  the  electric  current  was  a  great  triumph  for 
science.     Has  the  question  come  to  you  :  "  Can  hydrogen 
and  oxygen  in  their  turn  be  broken  up  into  some  other 
substances,  as  water  was?  '      The  answer  is  that  they 
have  never  been  broken  up,   up   to   the  present  time. 
A  substance  like  pure  water,  which  is  not  mixed  with 
something  else  and  which  has  at  least  two  kinds  of  matter 
combined  in  itself  is  called  a  compound.     A  kind  of  matter 
like  oxygen,  which  we  have  never  been  able  to  break  up, 
is  called  a  simple  substance,  or  an  element.     There  are 
probably  several  hundred  thousand  known  compounds. 
All  are  made  out  of  80  or  90  elements.     Most  contain 
only  2,  3,  or  4  of  these  elements.     In  the  same  way  we 
make  all  the  words  of  our  language  out  of  26  letters. 
Carbon  is  an  element,  too ;  also  iron,  nitrogen,  sulphur, 
mercury,  and  phosphorus. 

Mixtures  are  very  different  from  compounds.  Sugar  is  a  com- 
pound and  salt  is  a  compound,  but  when  the  two  are  powdered  and 
rubbed  together  we  get  a  mixture  of  these  two  compounds.  When 
sugar  and  sulphur  are  rubbed  together,  we  get  a  mixture  of  a  com- 
pound with  an  element.  When  powdered  iron  and  sulphur  are  rubbed 
together,  we  get  a  mixture  of  two  elements.  Soil  is  a  mixture  of  many 
substances.  Air  is  a  mixture  of  nitrogen,  oxygen,  water  vapor,  carbon 
dioxide,  and  small  amounts  of  other  gases  (cf.  §  26). 

114.  How  Can  We  Prepare  Hydrogen?  —  If  we  want 
to  get  some  hydrogen  for  study,  we  might  get  it  out  of 
water,  by  the  action  of  the  electric  current ;  but  there  are 
easier  ways.     You  remember  how  marble  foamed  when 
you  put  hydrochloric  acid  upon  it  (cf.  §38).     The  gas 


SUBSTANCES 


131 


given  off  was  carbon  dioxide.  When  "  dilute  "  hydro- 
chloric acid  (that  is,  hydrochloric  acid  mixed  with  much 
water)  is  put  upon  zinc  or  iron,  a  similar  foaming  takes 
place,  but  in  this  case  the  gas  is  hydrogen.  The  hydrogen 
is  present  in  the  acid ;  the  action  of  the  metal  sets  the 
hydrogen  free  as  an  element. 


a.  b. 

FIG.  75,  a  and  6.  —  Hydrogen  being  prepared  from  zinc  and  a  dilute  acid. 
It  may  be  collected  "over  water"  or  "over  air." 

Put  some  bits  of  zinc  in  a  glass  tube  (test  tube)  or  a  small  wide- 
mouthed  bottle  (see  Fig.  22),  and  cover  the  zinc  with  dilute  hydro- 
chloric or  sulphuric  acid.  See  how  the  liquid  foams,  owing  to  the 
escape  of  tiny  hydrogen  bubbles.  If  the  zinc  does  not  act  rapidly 
with  the  acid,  pour  off  the  acid  and  cover  the  zinc  with  a  dilute  solu- 
tion of  blue  vitriol  (copper  sulphate) ;  after  a  few  moments  pour  the 
solution  off.  The  zinc  will  then  be  covered  with  a  thin,  black  coating 
of  copper.  If  you  now  add  the  acid  to  the  zinc,  the  two  will  act  rapidly. 
When  the  mixture  is  foaming,  apply  a  match  to  the  mouth  of  the 
test  tube.  Be  careful.  Do  you  get  any  evidence  that  hydrogen 
burns  ? 

We  can  prepare  more  hydrogen  in  a  bottle  which  is  fitted  with  a 
two-hole  stopper,  a  "  thistle  "  tube,  and  a  delivery  tube  reaching  into 
a  water  pan  (Fig.  75,  a).  The  thistle  tube  allows  us  to  add  fresh 


132  JUNIOR  SCIENCE 

supplies  of  the  acid ;  it  also  lets  the  hydrogen  escape  if  the  delivery 
tube  is  stopped  up.  Hydrogen  is  collected  over  water,  as  oxygen  is, 
because  only  a  little  dissolves  in  the  water. 

We  can  also  collect  hydrogen  "  over  air,"  as  is  shown 
in  Fig.  75,  6.  Do  you  think  from  this  fact  that  it  is 
lighter,  or  heavier,  than  air? 

115.  What  is  Hydrogen  Like  ?  —  If  you  have  collected 
hydrogen  "  over  air,"  you  have  learned  that  it  is  as  color- 
less as  air  and  oxygen.  As  we  make  it,  it  has  an  odor, 

but  the  pure  gas  is  odorless.  It 
is  the  lightest  gas  known :  air 
is  14.4  times  as  heavy  as  hy- 
drogen ;  oxygen  is  16  times  as 
heavy ;  carbon  dioxide  is  22  times 
as  heavy.  It  would  take  15 
gallons  of  hydrogen  to  weigh  as 

FIG.  76.  —  Filling  soap  bub-    *  J 

bies  with  hydrogen,    why  do  much  as  a  nickel  five-cent  piece 

(5  grams). 

One  way  to  show  how  light  hydrogen  is,  is  to  fill  soap 
bubbles  with  it  (Fig.  76).  For  this  purpose  a  clay  pipe 
may  be  used  instead  of  a  delivery  tube.  The  bubbles 
will  rise  rapidly.  Do  you  suppose  hydrogen  would  be 
useful  in  the  making  of  airships  and  balloons  ? 

If  you  collect  a  bottle  of  hydrogen,  as  is  shown  in  §  114,  you  can 
find  out  whether  hydrogen  allows  wood  to  burn  in  it,  as  oxygen  did. 
First  let  the  hydrogen  escape  for  a  minute  or  two  from  the  bottle  in 
which  it  is  being  prepared,  so  as  to  make  sure  that  the  air  that  was 
in  the  bottle  at  first  has  been  swept  out.  Then  collect  a  bottleful  of 
hydrogen  "  over  water/'  Now  raise  the  bottle  of  gas,  keeping  the 
bottle  mouth  downward,  and  put  a  burning  splinter  up  into  the  bottle. 
There  will  be  a  slight  "  pop  "  as  the  hydrogen  is  set  on  fire  at  the 


SUBSTANCES 


133 


Burning^ 
Hydrogen 


mouth  of  the  bottle,  but  the  flame  on  the  splinter  up  in  the  bottle 
will  be  put  out.  This  shows  that  hydrogen  burns  where  it  can  get 
at  the  oxygen  of  the  air,  but  wood  does  not  burn  in,  or  unite  with,  the 
hydrogen  as  it  does  with  oxygen.  A  burning  candle,  a  burning  strip 
of  paper,  or  a  burning  wick  containing  kerosene  would  all  act  as  the 
wood  does.  We  say  that  hydrogen  "  burns,  but  does  not  support 
combustion."  Hydrogen  is  not  poisonous.  Do  you  think  we  could 
breathe  it  instead  of  oxygen? 

116.   What  Is  Formed  When  Hydrogen  Bums  ?  — We 

learned  in  §  27  that  when  a  substance  burns  in  the  air, 

it  unites  with  oxygen  ;  we  also 

learned    in    §  112    that    when 

water   is    broken    up    by   the 

electric   current,    its    elements 

are  found  to  be  hydrogen  and 

oxygen.  What  substance,  then, 

might  we  expect  to  be  formed 

when  hydrogen  burns  in  air  ? 

If  you  wish  to  light  a  jet 
of  hydrogen,  you  must  take 
care  that  the  hydrogen  is  not 
mixed  with  air.  If  it  is  mixed 
with  air,  there  will  be  a  vio- 
lent explosion  when  the  flame 
is  brought  near  it,  and  the 
glass  may  be  blown  into  your 
face.  So  be  sure  to  make  the  following  test  for  hydrogen  : 

Safety  Test  for  Hydrogen.  —  First  be  sure  that  the  gas  is  coming 
off  rapidly.  Put  a  test  tube  down  over  the  outlet  tube,  as  in  Fig.  75,  6, 
for  a  full  minute ;  now  carry  the  tube,  with  its  mouth  downward,  to 
a  flame  at  least  3  feel  away.  Finally  carry  the  test  tube,  still  with 


Water 


FIG.  77.  —  Burning  hydrogen. 
Before  lighting  the  gas  be  sure 
to  make  the  "safety  test."  As 
the  hydrogen  burns,  a  fog  forms 
on  the  inside  of  the  beaker  and 
finally  water  drops  from  the  edge 
of  the  beaker.  With  what  element 
does  hydrogen  unite  when  it 
burns  ? 


134  JUNIOR  SCIENCE 

its  mouth  downward,  back  to  the  jet  of  hydrogen.     Repeat  the  test 
until  the  test  tube  of  burning  hydrogen  sets  the  jet  on  fire  (Fig.  77). 

You  will  find  that  the  flame  is  nearly  colorless,  but  very 
hot.  If  we  put  over  the  jet  of  burning  hydrogen  a  large 
glass  or  bottle,  the  inside  will  soon  be  covered  with  a 
watery  mist ;  after  a  while  drops  of  water  run  down  and 
drip  from  the  mouth  of  the  jar  So  it  is  water  that  is 
formed  when  hydrogen  burns  in  air.  After  the  hydrogen 
has  heated  the  tip  of  the  glass,  the  flame  becomes  yellow. 
This  is  due  to  an  element  named  sodium,  which  is  part  of 
the  glass. 

117.  Do  Our  Fuels  Contain  Hydrogen  ?  —  Put  a  bright 
tin  saucepan  of  cold  water  over  a  gas  burner,  or  a  gas 
stove.     Make  sure  that  the  outside  is  perfectly  dry  and 
that  the  dish  does  not  leak.     If  possible,  put  a  second 
dish  over  an  alcohol  lamp  or  over  the  chimney  of  a 
kerosene  lamp.     What  is  deposited  over  the  bottom  and 
the  sides  of  the  dish?     Can  it  be  water?     Where  did  it 
come  from?     This  experiment  shows  us  that  the  gas, 
alcohol,  and  kerosene  contain  hydrogen.     When  they  are 
burned,  their  hydrogen  unites  with  the  oxygen  of  the 
air  to  form  water.     The  carbon  they  contain  burns  to 
form  carbon  dioxide.     This  is  not  condensed  by  the  cold 
dish.     So  in  most  of  our  fuels  we  are  really  burning  hy- 
drogen as  well  as  carbon,  and  water  is  formed  as  well  as 
carbon  dioxide. 

118.  Is  Salt  an  Element?  —  All  of  us  know  something 
of  salt,  the  substance  we  use  in  seasoning  our  food  and 
in  preserving  certain  foods,   such  as  salted  meats  and 
fish.     It  is  found  in  large  amounts  in 'sea  water  and  in 


SUBSTANCES  135 

salt  water;  it  is  also  found  in  layers  in  the  earth,  as 
rock  salt.  We  obtain  salt  from  salt  water  by  letting  the 
sun  evaporate  the  water,  or  by  boiling  it  off  over  a  fire. 

Perform  this  experiment:  Dissolve  as  much  salt  as  possible  in  a 
small  amount  of  clear  water  and  let  a  thin  layer  of  this  solution  stand 
in  a  shallow  dish  until  the  water  evaporates.  If  you  examine  the 


(From  Hopkins'  Physical  Geography.) 
FIG.  78.  —  The  preparation  of  salt  for  our  use  is  a  great  industry. 

lumps  of  salt  left,  especially  with  a  magnifying  glass,  you  will  find  that 
they. are  cubes  and  that  they  are  arranged  in  masses  that  are  "hopper 
shaped/'  that  is,  like  a  four-sided  funnel.  When  a  substance  separates 
from  a  solution  in  regular  shapes,  it  is  said  to  crystallize,  and  the  regular- 
shaped  masses  which  it  forms  are  called  crystals.  In  salt  these  crystals 
are  often  very  large.  You  have  also  seen  crystals  of  sugar.  Large 
sugar  crystals  we  call  "  rock  candy  "  (Fig.  79). 


136 


JUNIOR  SCIENCE 


If  we  heat  salt,  we  find  we  cannot  change  it,  even  at 
red  heat.  If  the  salt  is  heated  white  hot,  it  melts,  as 
ice  does  at  0°  C.  When  men  passed  an  electric  current 
through  melted  salt,  an  interesting  change  took  place. 
At  one  pole  there  was  found  a  shining  metal,  looking  like 
silver.  This  is  called  sodium.  At  the  other  pole  there 
appeared  a  greenish-yellow  gas  called  chlorine  (chlor'in). 
When  the  sodium  is  cold,  it  is  solid,  but  it  is  so  soft  that 
it  can  be  cut  like  wax.  Thus  we  see  that  just  as  we  can 
separate  water  into  two  elements,  hydrogen  and  oxygen, 


Salt  Alum  Sugar  Quartz: 

FIG.  79.  —  Crystals  of  salt,  alum,    sugar,    and    quartz.     Note    the   beautiful 
forms  in  which  matter  arranges  itself. 

so  we  can  separate  salt  into  sodium  and  chlorine.  The 
chemist  calls  salt,  sodium  chloride,  to  show  that  it  con- 
tains sodium  and  chlorine.  What  might  water  be  called  ? 
Review  §  32. 

Just  as  we  can  cause  hydrogen  and  oxygen  to  reunite 
to  form  water,  so  we  can  get  sodium  and  chlorine  to  form 
salt.  If  a  thin  shaving  of  sodium  is  put  into  chlorine, 
the  shiny  sodium  and  the  green  chlorine  disappear, 
leaving  white  salt  in  their  place. 

119.  What  is  Sulphur  Like?  —  Examine  some  of  the 
substance  known  as  sulphur,  or  "  brimstone. "  It  is  a 
yellow  solid  having  no  odor.  Sulphur  does  not  dissolve 
in  water  or  in  the  mouth ;  so  it  has  no  taste.  If  you 


SUBSTANCES  137 

drop  a  lump  into  water,  it  will  sink,  because  its  density 
is  greater  than  water. 

If  you  heat  some  sulphur  carefully  in  a  test  tube  or  porcelain  dish, 
you  find  that  it  melts  to  form  a  light-yellow  liquid  which  is  easily 
poured.  As  you  heat  it  hotter,  the  sulphur  becomes  darker  and  harder 
to  pour.  Heat  it  still  hotter  and  you  will  find  it  remains  dark  in  color, 
but  can  now  be  poured.  If  you  boil  the  sulphur,  you  will  see  that  its 
vapor  is  light  brown.  If  you  pour  the  boiling  sulphur  into  cold  water, 
you  will  get  an  elastic  solid.  This  is  still  sulphur,  but  it  changes  back 
to  its  original  form  very  slowly. 

Sulphur  is  an  element,  so  neither  heat,  nor  electricity, 
nor  any  other  means  we  know  of,  will  break  it  up  into 
anything  else.  It  burns  when  heated  to  its  kindling 
temperature,  forming  sulphur  dioxide  (cf.  §  24),  a  gas 
with  a  sharp  odor.  We  often  get  this  odor  when  a  match 
is  struck,  because  of  the  sulphur  in  the  match  head. 
Sulphur  combines  with  many  metals,  even  when  they 
are  simply  rubbed  with  it. 

Clean  a  one-cent  piece  with  gasolene  and  rub  it  dry, 
then  put  on  it  a  bit  of  sulphur  and  rub  the  two  together. 
The  black  spot  which  appears  is  copper  sulphide.  If 
we  know  that  there  is  sulphur  in  eggs,  can  you  tell  why 
silver  egg  spoons  become  black  ? 

The  sulphur  in  the  United  States  is  obtained  in  Louisi- 
ana, where  there  is  a  deposit  half  a  mile  in  diameter. 
Some  is  also  found  in  Texas  and  California.  Europe  gets 
most  of  its  supply  from  Sicily. 

120.  What  is  Phosphorus  Like?  —  We  have  already 
learned  something  of  the  element  phosphorus,  of  the 
great  activity  of  the  yellow  form,  and  of  the  power  of 


138  JUNIOR  SCIENCE 

burning  phosphorus  to  remove  all  the  oxygen  from  a 
bottle  of  air.  Phosphorus  is  one  of  the  elements  neces- 
sary for  the  bodies  of  animals.  When  the  bones  of  an 
animal  are  burned,  a  compound  of  calcium,  phosphorus, 
and  oxygen  (calcium  phosphate)  forms  a  large  part  of 
the  ashes.  It  is  out  of  these  bone  ashes  and  out  of 
natural  calcium  phosphate  found  as  a  rock  that  phos- 
phorus is  made. 

Yellow  phosphorus  unites  readily  with  oxygen,  even 
when  it  is  cold ;  in  doing  so  it  gives  off  light.  You  have 
seen  the  bright  streak  left  when  phosphorus  matches  are 
struck  in  the  dark.  The  name  phosphorescence,  meaning 
"  producing  of  bright  light/'  is  applied  to  this.  Yellow 
phosphorus  is  used  as  a  poison  for  rats  and  other  vermin, 
as  well  as  in  matches.  Red  phosphorus  is  used  in  the 
making  of  safety  matches. 

121.  What  is  a  Match?  — We  rarely  think  of  the 
convenience  of  having  matches  until  we  are  without 
them.  Matches  were  first  made  in  1827.  They  "  work  " 
because  phosphorus  is  easily  set  on  fire  by  rubbing 
(friction),  if  there  is  present  a  substance  to  give  it 
oxygen.  The  "  parlor "  match,  which  can  be  struck 
anywhere,  has  a  tip  containing  yellow  phosphorus, 
paraffin,  or  sulphur,  and  an  oxidizing  substance  like 
potassium  chlorate  or  red  lead.  Glue  is  used  to  make 
the  substances  stick  to  the  splinter.  When  the  match 
is  rubbed  or  struck,  the  phosphorus  unites  with  the 
oxygen  of  the  potassium  chlorate  or  red  lead.  The 
heat  produced  by  the  burning  of  the  phosphorus  sets 
the  paraffin  or  sulphur  on  fire  and  the  heat  from  this 


SUBSTANCES  139 

fire  heats  the  wood  to  the  temperature  at  which  it  begins 
to  burn. 

Safety  matches  are  not  so  convenient  as  parlor  matches  because 
they  must  be  struck  on  the  box.  The  surface  of  the  box  contains  the 
phosphorus ;  it  is  red  phosphorus  instead  of  the  yellow  form.  When 
the  tip  of  the  match  is  rubbed  against  the  surface  of  the  box,  a  little 
of  the  red  phosphorus  is  changed  to  the  yellow,  and  the  burning  of 
this  substance  starts  the  burning  of  the  match  tip. 

The  use  of  yellow  phosphorus  for  matches  is  forbidden 
in  many  countries  of  Europe.  Its  use  is  prevented  in 
the  United  States  by  a  tax  on  matches  containing  it. 
The  reason  why  matches  containing  yellow  phosphorus 
are  not  wanted  is,  first,  that  they  are  easily  set  on  fire  by 
careless  handling,  by  children,  and  even  by  rats  and  mice. 
Great  fire  losses  occur  where  parlor  matches  are  used. 
A  second  reason  is  that  the  vapor  from  them  is  dan- 
gerous to  the  workmen  who  make  or  handle  them. 

"  Strike  anywhere  "  matches  are  now  being  made  with 
a  compound  of  phosphorus  and  sulphur  (phosphorus 
sulphide)  which  does  not  give  off  the  vapor  of  phosphorus 
and  which  is  not  so  easily  set  on  fire  as  phosphorus  itself. 

What  a  great  deal  of  science  there  is  in  the  striking  of 
a  match ! 

122.  Exercises. —  1.  Read  a  recipe  for  the  making  of  johnny- 
cake.  Is  johnny-cake  a  mixture  or  a  compound?  What  reason  have 
you  for  thinking  that  wood  is  not  an  element? 

2.  Judging  from  the  names  of  the  following  compounds,  tell  what 
elements  are  in  each :  lead  sulphide,  iron  oxide,  carbon  dioxide,  sodium 
chloride. 

3.  If  you  had  a  bottle  of  carbon  dioxide  and  one  of  hydrogen,  how 
could  you  tell  which  was  which? 


140  JUNIOR  SCIENCE 

4.  When  you  put  a  cold  lamp  chimney  upon  a  lighted  kerosene 
lamp,  the  inside  of  the  chimney  becomes  covered  with  mist.     What 
substance  is  the  mist?     Where  does  it  come  from?     Why  does  the 
bottom  of  a  teakettle  filled  with  cold  water  become  wet  when  you  put 
it  over  a  gas  flame? 

5.  Name  several  uses  of  salt. 

6.  How  has  civilization  been  helped  by  the  invention  of  matches  ? 


CHAPTER  XIV 
WATER 

123.  Where  Is  Water  Found?  —  How  much  there  is 
to  know  about  the  common  substance  "  water  "  !  You 
think  of  it  as  a  liquid  that  flows  from  hydrants  or  is 
pumped  from  wells,  or  that  flows  in  streams,  from  the 
little  springs  and  brooks  to  the  great  rivers  of  the  earth ; 
you  think,  too,  of  ponds  and  lakes  and  the  mighty  oceans. 
You  must  also  think  of  it  as  rain,  as  clouds,  as  ice  and 
snow,  as  the  invisible  water  vapor  that  rises  from  tea- 
kettles and  from  the  sea,  to  become  a  part  of  our  at- 
mosphere, until  it  condenses  and  returns  once  more  to 
the  earth's  surface.  Water  is  not  only  on  the  surface 
and  in  the  atmosphere,  but  in  the  rocks  as  well.  No 
matter  where  we  dig,  we  find  it,  even  in  the  desert. 
Water  is  a  large  part  of  all  plants  and  animals  as  well 
as  of  our  food.  The  following  table  shows  how  much  of 
it  there  is  in  our  bodies  and  in  some  of  our  foods : 

PER  CENT  PER  CENT 

OF  WATER  OF  WATER 

Human  body  ....     70  Watermelon      ....     92 

Milk 87  White  bread     ....     35 

Potatoes 78  Beef 62 

The  farmer  looks  for  water  anxiously  in  the  growing 
season,  because  he  says,  "  No  one  ever  starved  in  a  wet 

141 


142  JUNIOR  SCIENCE 

year  "  ;  the  scientist  says :     "  There  is  no  life  without 
water. " 

124.  What  is  Water  Like?  —  We  already  know  some- 
thing of  what  water  is  like.  In  a  small  amount  it  is 
without  color,  but  a  large  amount  of  it  looks  blue.  Our 
drinking  water  has  a  taste,  because  of  substances  dis- 
solved in  it,  but  water  that  has  nothing  in  it  is  tasteless 
and  flat,  much  like  boiled  water.  We  have  learned  that 
the  boiling  point  of  water  is  100°  C.  and  is  used  as  a 
standard  mark  on  the  thermometer,  as  is  also  its  freez- 
ing point,  0°  C.  A  cubic  foot  of  water  weighs  about 
62.5  pounds  and  a  cubic  centimeter  of  it  at  4°  C.  weighs 
one  gram.  If  you  put  warm  water  in  a  flask  with  a 
very  small  neck  and  cool  the  flask,  the  water  shrinks  in 
volume  until  its  temperature  is  4°  C.  (39°  F.) ;  then  it 
expands  until  its  temperature  is  0°  C.  Water  is  there- 
fore most  dense,  or  heavy,  at  4°  C.  and  not  at  0°  C. 
Because  of  this  fact  the  water  at  the  bottom  of  lakes  is 
rarely  cooled  lower  than  4°  C. ;  for  if  it  becomes  colder, 
it  expands,  and  rises  instead  of  sinking.  When  water 
freezes,  it  expands,  so  that  100  cubic  feet  of  water  become 
109  cubic  feet  of  ice.  So  when  we  have  ice  at  the  top,  we 
have  water  near  0°  C.  just  under  the  ice,  and  water  near 
4°  C.  at  the  bottom.  Because  this  is  so,  water  animals 
and  plants  can  live  through  the  winter  and  in  the  deep 
waters  of  the  frigid  zone.  Ice,  like  water,  is  blue  in  large 
masses. 

You  know  how  readily  salt,  sugar,  soda,  and  many 
other  substances  disappear  in  water;  we  say  they  dis- 
solve, and  that  water  is  the  solvent.  Other  liquids,  such 


WATER  143 

as  alcohol,  are  used  to  dissolve  substances  which  water 
cannot,  but  water  is  our  most  common  solvent. 

Hold  a  lump  of  sugar  so  that  its  lower  side  just  touches  the  surface 
of  some  water  in  a  clear  glass  and  watch  the  appearance  of  the  liquid. 
The  oily  appearance  is  caused  by  the  sinking  of  the  sugar  solution 
before  it  has  mixed  with  the  rest  of  the  water.  Do  the  same  with  a 
lump  of  copper  sulphate  (bluestone  or  blue  vitriol).  Are  the  solutions 
of  sugar  and  blue  vitriol  heavier  or  lighter  than  the  water  used? 
What  are  the  colors  of  the  solutions? 

125.  How  Does  Water  Boil?  —  Watch  the  water  in  a 
pan  as  it  nears  boiling.  At  first  there  are  tiny  bubbles 
that  escape ;  these  are  chiefly  air  that  was  dissolved  in 
the  water.  Then,  as  the  temperature  rises,  there  are 
larger  bubbles  of  steam  that  start  from  the  bottom,  but 
do  not  rise  to  the  top.  These  condense  and  cause  the 
"  singing  "  of  the  water,  but  the  water  is  not  yet  boiling. 
Finally  the  bubbles  rise  to  the  surface  and  burst ;  as 
they  do  so,  they  have  force  enough  to  push  out  the  air. 
The  bubbles  jump  up  and  down  when  there  is  real  boil- 
ing. Then  and  then  only,  will  a  thermometer  register 
the  boiling  point  of  water. 

We  must  remember  that  the  temperature  at  which  water  boils 
depends  on  how  heavily  the  atmosphere  presses  down  upon  the  water. 
As  we  ascend  a  mountain  and  leave  more  and  more  of  the  atmosphere 
below  us,  water  does  not  need  to  be  heated  so  hot  to  make  it  boil. 
The  steam  bubbles  do  not  need  to  haVe  as  much  force  to  push  away 
from  the  water  as  they  did  when  the  air  was  pressing  harder  upon  them. 
The  boiling  point  is  lowered  about  1°  C.  for  every  960  feet  we  ascend 
above  sea  level.  So  water  boils  at  92.3°  C.  at  Mexico  City,  7500  feet 
above  the  sea.  At  Denver,  5500  feet  high,  it  boils  at  about  95°  C.  At 
about  what  temperature  will  it  boil  on  Pikes  Peak,  14,108  feet  high? 


144  JUNIOR  SCIENCE 

126.  How  Is  Ice  Made?-- Years  ago  ice  was  carried 
to  tropical  countries  in  ships,  but  modern  methods  of 
living  require  so  much  ice  that  a  great  deal  of  our  ice  is 
manufactured,  even  in  temperate  zones.  How  can  we 
make  ice  in  summer?  We  have  already  learned  that 
the  reason  why  perspiration  cools  us  is  that  the  heat  needed 
to  evaporate  it  comes  from  our  bodies  (cf.  §  71).  Water 
evaporated  in  a  porous  jug  cools  the  water  inside. 

Substances  that  evaporate 
rapidly  can  be  made  to  take 
away  so  much  heat  that  very 
low  temperatures  can  be  ob- 
tained. Pour  out  a  little  ether 
into  a  shallow  pan,  such  as  the 
cover  of  a  baking-powder  can 
(Fig.  80),  set  it  on  a  few  drops 

FIG.  80.  —  By  causing  the  ether       /.  i         j  r    i  j    j 

to  evaporate  rapidly  you  can  freeze    Ol  Water  placed  On  SOme  folded 

the  water  under  the  pan.    Use  a  writing  paper,  and  by  means  of 

long  tube  and  perform  the  expen-  r    *       7 

ment  near  a  window  with  an  out-    a  tube  and  belloWS  (your  cheeks 

will  serve  as  bellows)  force  air 

rapidly  through  the  ether.  The  dish  can  be  frozen  to 
the  paper !  The  principle  of  rapid  evaporation  is  used  to 
make  artificial  ice.  Think  what  a  blessing  it  is  that  hot 
countries  can  have  ice  for  keeping  food  and  water  cool. 
The  liquid  that  is  used  to  freeze  water  is  liquid  ammonia. 
This  is  not  ammonia  water,  but  the  gas  ammonia  which  has 
been  strongly  compressed  until  it  turns  to  the  liquid  state. 

Usually  the  liquid  ammonia  is  made  in  strong  pipes  (Fig.  81). 
When  the  gas  is  compressed  into  the  liquid  form,  it  becomes  hot ;  so 
men  cool  it  by  spraying  running  water  over  the  pipes  which  hold  the 


WATER 


145 


ammonia.  Now,  when  the  pressure  is  removed,  the  ammonia  boils 
vigorously  and  in  so  doing  takes  up  a  great  deal  of  heat ;  for  just  as 
much  heat  is  needed  to  turn  the  liquid  ammonia  back  into  the  am- 
monia gas,  as  was  given  off  by  the  gas  when  it  was  compressed  to  a 
liquid.  So  the  pipes  become  very  cold,  and  when  they  are  run  through 
a  salt  brine,  they  cool  it  to  perhaps  -15°  C.  This  cold  salt  brine  is 
used  for  cooling  purposes,  just  as  hot  water  is  used  for  heating.  If 
we  put  it  around  molds,  or  tanks  of  water,  heat  is  taken  from  the 
water  until  it  is  frozen  (Fig.  81).  Cold  brine  is  also  used  in  cold-storage 


Cold  Water 


u         .  .      „  <~old  Water  ,  Spray 

Hot    Ammonia    Gas       to  Condensej^the  A 


Sprays 

>mmonia  Gas 


Compresssion  Pump 


Expansion  Coils  and  Ice  Molds 


FIG.  81.  —  When  liquid  ammonia  is  allowed  to  boil  rapidly,  it  takes  up  heat 
from  the  salt  brine  and  thus  cools  it  below  the  freezing  point  of  water. 

warehouses  and  in  refrigerator  cars  to  produce  a  low  temperature. 
In  this  way  butter,  eggs,  meat,  and  fruits  are  kept  cold  to  prevent  their 
spoiling  (Fig.  82). 

127.  How  Is  Ice  Cream  Frozen? --You  know  how 
ice  cream  is  made.  The  cream  is  placed  in  a  pail  sur- 
rounded by  a  mixture  of  salt  and  ice.  As  the  freezer 
is  turned,  the  cream  comes  in  contact  with  the  cold  walls 
of  the  pail  and  is  frozen.  But  why  does  a  mixture  of 
ice  and  salt  give  a  colder  temperature  than  ice  alone  ? 


146  JUNIOR  SCIENCE 

When  we  draw  water  from  a  faucet  and  put  ice  into 
it,  the  ice  melts.  Where  does  the  heat  come  from  that 
is  needed  to  melt  the  ice  ?  It  comes  from  the  water ; 
therefore  the  water  is  cooled,  if  there  is  enough  ice,  to  0°  C., 
which  is  the  temperature  of  melting  ice  or  freezing  water. 


FIG.  82.  —  Rooms  in  which  meats  and  other  perishable   goods  are   kept  are 
cooled  by  pipes  carrying  cold  brine. 

What  happens  when  we  put  salt  upon  ice?  The  ice 
begins  to  melt,  forming  water,  and  the  salt  dissolves  in 
the  water,  producing  a  salt  solution,  or  salt  brine.  The 
ice  is  really  melting  in  salt  brine.  The  heat  needed  to 
keep  up  the  melting  comes  from  the  brine.  But  as  salt 
brine  does  not  freeze  until  it  is  cooled  to  about  — 20°  C., 
the  melting  of  the  ice  will  continue  until  this  temperature 
is  reached.  Now,  while  a  temperature  of  0°  C.  is  not 
low  enough  to  freeze  cream,  one  of  —20°  C.  is. 

How  is  the  making  of  artificial  ice  different  from  the 


WATER  147 

freezing  of  cream?  In  the  making  of  ice  we  produce  a 
cold  brine  by  the  rapid  boiling  of  liquid  ammonia;  in 
freezing  ice  cream  we  cool  the  brine  by  the  rapid  melting 
of  ice  in  the  brine. 

128.  How  Do  Bodies  of  Water  Affect  Climate  ?- 
Have  you  ever  wondered  why  peaches  are  grown  so  suc- 
cessfully in  the  "  peach  belt  "  on  the  eastern  shore  of 
Lake  Michigan,  while  they  cannot  be  grown  success- 
fully at  many  places  that  are  much  farther  south,  but 
away  from  the  water?  Can  you  tell  why  grapes  are 
grown  in  large  quantities  on  the  eastern  and  southeastern 
shores  of  Lake  Erie,  in  New  York,  Pennsylvania,  and 
Ohio?  The  answer  is  found  in  a  peculiar  quality,  or 
property,  of  water. 

If  you  try  to  heat  a  pound  of  water  and  a  pound  of 
iron  over  two  burners  giving  the  same  amount  of  heat, 
the  iron  reaches  100°  C.  long  before  the  water  does.  But 
when  you  stop  heating  them,  the  iron  cools  much  more 
rapidly  than  the  water.  If  you  have  a  pound  of  iron  and 
one  of  hot  water,  both  at  100°,  and  put  each  separately 
into  a  pan  of  ice,  the  heat  in  the  water  will  melt  about 
9  times  as  much  ice  as  the  heat  in  the  iron  will.  We  say 
that  water  has  a  greater  heat  capacity  than  the  iron  has. 
Now  the  land,  like  iron,  has  a  small  heat  capacity.  Be- 
cause of  this  it  is  heated  up  more  rapidly  by  the  sun 
than  water  is,  but  it  also  cools  more  rapidly.  So  a 
place  that  is  inland,  or  away  from  the  water,  has  great 
extremes  of  heat  and  cold,  while  a  place  near  a  large 
body  of  water  is  kept  warmer  in  winter  and  cooler  in 
summer  by  the  presence  of  the  water. 


148  JUNIOR  SCIENCE 

We  can  now  answer  the  question  regarding  the  peach 
orchards  on  the  eastern  shore  of  Lake  Michigan  and  the 
grape  vineyards  on  the  southeastern  shore  of  Lake  Erie. 
The  prevailing  cold  winds  of  the  winter  in  the  region  of 
the  Great  Lakes  are  from  the  northwest,  and  the  winds 
are  warmed  as  they  pass  over  these  large  bodies  of  water. 
As  a  result  the  weather  of  winter  is  less  severe  on  the 
eastern  shores  than  on  the  western  shores  of  these  lakes. 

Why  is  the  eastern  shore  of  Lake  Michigan  dotted  with 
summer  resorts?  Why  do  people  go  to  the  shore  of  the 
ocean  in  hot  weather  ? 

This  effect  of  water  upon  the  land  is  much  greater  if  currents  of 
cold  or  of  warm  water  flow  along  the  shore.  Thus  the  shores  of 
Alaska,  British  Columbia,  and  the  Pacific  Northwest  have  a  mild 
winter  climate,  owing  to  the  Japan  current  which  passes  along  the 
coast.  The  Gulf  Stream,  containing  warm  water,  carries  heat  from 
the  tropics  up  to  the  western  coast  of  Europe  and  keeps  open  water 
in  the  most  northern  Norwegian  ports. 

129.  How  Does  Water  Change  the  Earth's  Surface  ?- 
Did  you  ever  wonder  what  becomes  of  all  the  rain? 
About  35,000  cubic  miles  of  it  fall  upon  the  land  every 
year.  This  is  nearly  seven  times  as  much  water  as  is 
stored  in  our  Great  Lakes.  The  rain  that  falls  upon 
the  earth  and  washes  away  the  soil,  the  crystals  of  frost 
that  freeze  within  the  cracks  of  the  rocks  and  burst  the 
rocks  apart,  the  great  sheets  of  snow  and  ice  that  have 
moved  over  large  areas  of  the  earth  —  these  have  chiseled 
the  land  into  its  present  forms.  Water  is  thus  not  only 
the  storehouse  of  the  sun's  heat,  but  also  the  great  sculptor 
of  the  earth's  surface. 


WATER  149 

You  have  heard  of  the  Grand  Canon  of  the  Colorado  River  and  of 
other  deep  canons,  or  gorges,  like  it  (Fig.  83).  The  Grand  Canon  is 
217  miles  long,  8  to  15  miles  wide,  and  a  mile  deep.  Do  you  think  that 
the  river  just  ran  down  into  a  deep  crack  in  the  mountains  and  took 
it  for  its  bed?  No ;  the  river  itself  dug  its  own  bed  by  wearing  away 
the  rock  little  by  little,  century  after  century.  The  Ohio  has  carried 
the  wearing-away  process  farther  and  flows  through  a  peaceful  valley 
bordered  by  rounded  hills ;  the  Mississippi,  Nile,  and  Hoang-Ho  have 
worn  down  their  valleys  to  low,  fertile  flood  plains,  but  little  above  sea 
level.  What  force  causes  water  to  fall  and  to  run  downhill  to  the  sea? 
What  lifted  the  water  to  the  mountain  tops  ? 

Why  is  it  that  the  seashore  is  so  interesting  to  you? 
Because  there  are  long  stretches  of  sandy  beaches,  great 
waves,  and  ships  on  long  voyages.  The  shoreline  is  a 
place  of  great  interest  to  the  scientist  also.  There  the 
land  and  sea  meet  and  carry  on  their  agelong  struggle  for 
the  possession  of  the  dry  ground.  The  rain  wears  away 
the  land,  the  rivers  carry  their  sediments  to  the  sea,  and 
the  sea,  not  satisfied  with  the  work  of  its  allies,  the  rain 
and  the  rivers,  pounds  away  at  the  shore  itself,  slowly 
cutting  it  away,  so  as  to  extend  the  empire  of  water. 
Which  will  win?  The  average  height  of  the  continents 
above  sea  level  is  about  2300  feet ;  but  the  average  depth 
of  the  sea  is  about  six  times  as  great,  or  13,000  feet.  So, 
if  the  sea  could  get  the  complete  mastery,  its  waters  could 
cover  all  the  land  with  a  layer  of  water  about  two  miles 
deep. 

130.  Exercises.  —  1.  Explain  why  water  is  believed  to  be  a  com- 
pound rather  than  an  element. 

2.  Is  a  cubic  foot  of  water  heavier,  or  lighter,  than  a  cubic  foot  of 
ice?  How  do  you  know? 


150 


JUNIOR  SCIENCE 


(From  Hopkins'  Physical  Geography.) 
FIG.  83.  —  In  the  Canon  of  the  North  Platte  River,  south  of  Casper,  Wyoming. 


WATER  151 

3.  Do  lakes  and  ponds  generally  freeze  to  the  bottom?    Would 
they  be  more,  or  less,  likely  to,  if  ice  were  heavier  than  water? 

4.  How  is  salt  commonly  obtained  from  salt  water? 

5.  Do  you  suppose  any  substances  besides  water  act  as  solvents? 
What  is  the  solvent  used  in  most  medicines? 

6.  When  the  water  used  for  cooking  potatoes  has  begun  boiling, 
will  the  potatoes  be  cooked  more  quickly,  if  there  are  two  burners 
instead  of  one  under  the  boiling  water? 

7.  Is  any  dessert  made  by  freezing  flavored  water  instead  of  cream  ? 

8.  Wliat  causes  the  bursting  of  water  pipes  in  winter?    Why  are 
hydrants  sometimes  left  turned  on  a  little  during  a  very  cold  night  ? 

9.  Why  is  it  easier  to  swim  in  the  ocean  than  in  fresh  water? 

10.   How  does  the  freezing  of  the  ground  help  to  break  it  up  for  the 
next  year's  crops? 


CHAPTER  XV 
WATER  SUPPLY  AND   SEWERAGE 

131.  Why  Do  We  Need  So  Much  Water  ?  —  Have  you 
ever  thought  how  much  we  depend  upon  an  abundant  sup- 
ply of  water?     In  our  homes  we  need  it  for  bathing,  for 
cooking  and  for  drinking,  for  washing  dishes  and  clothing, 
for  spraying  lawns  and  gardens  and  to  carry  waste  ma- 
terial into  the  sewerage  system.     As  ice  it  preserves  our 
food  and  with  salt  makes  our  common  freezing  mixture. 

Industries  need  water  to  furnish  steam  power  for  ma- 
chinery. Some  industries,  like  refineries  for  petroleum 
and  sugar,  as  well  as  laundries,  tanneries,  slaughter 
houses,  starch  factories,  gas  works,  paper  mills,  and  dye 
works,  need  it  for  washing  and  rinsing  on  a  large  scale. 
Cities  need  water  for  fire  protection  and  for  cleaning 
streets  and  to  carry  away  sewage. 

132.  How  Do  Cities  Get  Their  Water?  — Have  you 
ever   seen   the  waterworks   of   your  community?     It  is 
necessary  that  water  shall  have  some  pressure  in  the 
pipes,  so  that  it  will  flow  from  the  faucets  rapidly  and 
will  rise  to  the  top  floors  of  buildings.     There  must  also 
be  enough  pressure  so  that  we  can  throw  a  powerful 
stream  of  water  in  case  of  fire.     Some  cities  get  their 
water   to   flow   by   a   "  gravity "    system.     This   means 
that  the  water  level  of  some  pure  stream,  reservoir,  or 

152 


WATER  SUPPLY  AND  SEWERAGE  153 

lake  near  the  city  is  higher  than  any  buildings  of  the 
city,  so  the  water  can  simply  flow  downhill  to  the  city 
and  up  into  its  buildings.  Denver  has  such  a  water 
supply.  If  a  gravity  system  is  not  possible,  water  is 
often  pumped  by  a  strong  steam  force  pump  up  into  a 
high  tank,  or  reservoir,  or  "  standpipe  "  ;  from  this  it 
can  flow  down  to  the  ground  and  up  into  buildings. 

You  have  seen  pictures  of  the  great  Roman  aqueducts,  by  which 
water  was  brought  to  the  city  of  Rome  from  distant  lakes  or  springs. 
New  York  City  now  receives  its  water  through  a  great  aqueduct  from 
the  Catskills,  90  miles  away.  At  one  place  the  water  is  carried  under 
the  Hudson  River.  Los  Angeles  gets  its  water  from  mountains  many 
miles  away.  The  cities  on  the  Great  Lakes  get  their  water  supply 
from  the  lakes.  As  the  sewage  from  the  city  may  pollute  the  water, 
the  "  intakes  "  (places  where  the  water  is  taken  in)  are  usually  several 
miles  from  the  shore.  Chicago  has  built  the  "  Drainage  Canal  " 
at  great  cost,  to  carry  water  from  Lake  Michigan  into  the  Illinois 
River ;  thus  it  sends  the  city's  sewage  into  the  Mississippi  instead  of 
letting  it  pollute  Lake  Michigan. 

133.  How  Do  We  Get  Water  in  the  Country?  — In 
the  country  we  get  water  from  cisterns,  wells,  or  springs. 
We  dig  wells,  not  to  strike  underground  streams  or 
"  veins  "  of  water,  but  to  make  holes  into  which  the 
"  groundwater "  can  run.  This  is  the  water  which 
saturates  the  ground  everywhere  below  certain  levels. 
You  can  see  how  this  is,  if  you  dig  a  hole  into  ground  that 
is  water-soaked  after  a  rain.  Deep  wells  are  not  dug, 
but  are  drilled,  that  is,  bored  through  soil  and  rock  until 
a  level  is  reached  at  which  good  water  in  sufficient  amounts 
enters  the  well.  The  deeper  a  well,  the  greater  is  the  area 
of  the  ground  from  which  its  water  will  be  collected  and 


154 


JUNIOR  SCIENCE 


the  more  likely  it  will  be  to  last  through  a  dry  season. 
Artesian  wells  are  deep  wells  drilled  through  a  layer  of 
rock  or  clay  which  holds  the  water  at  great  pressure. 
When  the  covering  is  pierced,  the  pressure  of  the  water 
forces  the  stream  to  the  top  of  the  well  and  sometimes 
high  into  the  air. 

Springs  have  a  different  origin.    When  water  soaks  into  the  ground 
until  it  reaches  a  layer  of  rock  or  clay  that  it  cannot  penetrate  very 


FIG.  84.  —  Water  soaks  through  the  porous  sand  until  it  reaches  the  compact 
clay  which  it  cannot  penetrate.  At  the  bottom  of  the  hill  a  spring  is  formed. 

easily,  it  will  collect  above  this  layer.  If  the  ground  is  sloping  and 
the  rock  layer  comes  near  the  surface,  as  on  a  hillside,  the  water 
bubbles  out  as  a  spring  (Fig.  84). 

134.  What  is  Plumbing?  —  How  much  does  your 
family  pay  for  water?  In  some  cities  you  pay  a  "  flat 
rate,"  that  is,  no  matter  how  much  you  use,  you  pay 
a  certain  sum.  In  other  places  a  meter  is  put  into  your 
house  to  measure  the  volume  of  water  which  flows  from 
the  street  main  into  your  plumbing  system.  "  Plumb- 
ing "  comes  from  the  Latin  word  for  "  lead " ;  the 


WATER  SUPPLY  AND  SEWERAGE 


155 


plumbing  includes  the  pipes,  the  faucets,  and  the  traps 
through  which  fresh  water  is  carried  into  the  house  and 
waste  water  is  carried  away  from  it.  Iron  pipes  as  well 
as  lead  ones  are  used  for  plumbing;  the  iron  is  "  gal- 
vanized/' or  covered  with  zinc,  to  prevent  rusting. 

Lead  is  used  because  it  does  not  rust  easily  and  can 
easily  be  bent  around  corners.  When  lead  pipes  are 
fresh,  the  lead  may  be  oxidized  to  compounds  that  dis- 
solve in  water.  These  may  cause  serious  sickness; 


FIG.  85.  —  The  faucet  on  the  left  is  "compression  bibb"  ;  the  handle  must 
be  turned  round  and  round  until  the  rubber  tip  closes  the  hole  below  it.  The 
faucet  in  the  middle  is  a  "Fuller"  faucet.  In  the  cut  the  faucet  is  open;  we 
close  it  by  pulling  the  handle  forward.  This  pulls  the  acorn-shaped  rubber 
"gasket"  forward,  so  that  it  closes  the  hole  through  which  the  water  escapes. 
The  figure  on  the  right  shows  a  "trap." 

hence  we  should  always  let  water  run  for  a  minute  from 
new  lead  pipes.  Old  lead  pipes  become  covered  inside 
with  a  coating  that  stops  further  action  of  the  water  upon 
the  lead. 

Faucets,  also  called  "  hydrants  "  or  "  bibbs,"  are  usually  made  of 
brass.  Two  forms  are  shown  in  Fig.  85. 

Did  you  ever  notice  the  waste  pipe  of  your  kitchen  sink?  A  trap 
(Fig.  85)  is  a  bend  in  the  waste  pipe ;  it  remains  full  of  water  and  thus 
forms  a  "  waterseal."  This  keeps  the  air  of  the  sewer  from  entering 
the  house.  Water  should  be  run  through  all  sinks  and  floor  drains 
every  day,  so  that  the  traps  may  be  kept  full  of  water. 


156 


JUNIOR  SCIENCE 


135.  What  is  a  Pump  ?  —  Water  is  often  raised  from  a 
cistern  or  well  by  means  of  a  pump.  The  common  pump 
(Fig.  86,  a)  first  removes  the  air  from  a  pipe  extending 
under  the  surface  of  the  water,  just  as  we  do  when  we  drink 
lemonade  through  a  straw.  The  air  pressure  forces  the 
water  up  to  the  piston  of  the  pump,  if  the  piston  is  not 


a.  b. 

FIG.  86.  —  a.  When  the  pump  handle  is  pushed  down,  the  piston  is  raised 
and  the  water  above  the  piston  is  lifted  to  the  level  of  the  spout  and  overflows. 
When  the  pump  handle  is  raised,  the  piston  is  pushed  down  and  its  valve  is 
opened,  while  the  "cylinder  valve"  is  closed.  6.  A  force  pump  throws  a 
constant  stream  of  water  because  of  the  compressed  air  in  the  air  chamber. 

too  high  above  the  water  level.  When  the  piston  is 
forced  down  by  the  next  stroke  of  the  pump  a  valve  in 
the  piston  is  pushed  open,  and  water  rushes  above  the 
piston.  When  the  piston  is  forced  up  once  more,  the 
water  pressure  above  it  closes  the  valve  and  the  water 
above  the  piston  is  lifted  to  the  height  of  the  spout. 
This  is  called  a  lift  pump  and  is  useful  for  the  height  to 
which  air  pressure  can  raise  water,  that  is,  for  anything 


WATER  SUPPLY  AND  SEWERAGE  157 

less  than  34  feet.     Lift  pumps  are  not  perfect  and  so 
can  rarely  raise  water  more  than  28  or  30  feet  (cf.  §  17). 

136.  What  is  a  Force  Pump  ?  —  Did  you  ever  watch 
a  fire  engine  in  action  when  it  was  pumping  water  upon 
a  fire?     A  fire  engine  is  an  example  of  a  force  pump 
(Fig.  86,  6). 

A  force  pump  has  no  valve  in  the  piston.  When  the  piston  is 
raised,  the  pressure  of  the  atmosphere  forces  the  water  into  the  pipe 
and  cylinder.  When  we  force  the  piston  down,  the  water  below  closes 
the  valve  in  the  cylinder.  The  water  cannot  go  up  or  down,  so  it 
goes  out  through  the  discharge  valve  into  a  tank  containing  some  air 
(air  chamber).  The  air  is  compressed  by  the  pressure  of  the  water 
forced  into  it.  When  the  piston  is  raised  once  more,  the  water 
forced  through  the  discharge  "  backs  up,"  closing  the  discharge  valve. 
When  we  force  the  piston  down  again,  the  process  is  repeated.  In 
a  force  pump  there  is  a  constant  stream  of  water,  for  the  reason  that 
between  the  strokes  of  the  piston,  when  the  piston  itself  is  not  forcing 
the  water  out,  the  pressure  in  the  air  chamber  does  so.  What  advan- 
tage has  a  force  pump  over  a  lift  pump? 

137.  What   are   the  Dangers  in  Water?  — What  is 

meant  by  "  pure  "  water?  That  depends  upon  the  use 
we  wish  to  make  of  it.  Natural  water  is  never  pure. 
You  can  see  that  if  the  soil  contains  substances  that  are 
soluble  in  water,  the  rain  that  has  flowed  through  it  will 
contain  some  of  these  substances  also.  Water  is  often 
roily,  or  cloudy,  because  of  tiny  particles  that  it  carries 
along  without  dissolving  them.  Much  of  this  matter 
is  carried  to  the  sea.  The  undissolved  particles  are 
dropped  as  a  sediment,  and  the  dissolved  substances  are 
left  when  the  sea  water  evaporates.  There  are  nearly 
2.5  pounds  of  salt  in  every  100  pounds  of  sea  water,  and 


158 


JUNIOR  SCIENCE 


much  more  in  such  bodies  as  the  Dead  Sea  and  the  Great 
Salt  Lake. 

If  we  want  to  use  water  for  drinking,  we  do  not  worry 
much  over  the  dissolved  gases  and  minerals,  but  we  are 
careful  to  find  out  about  its  injurious  bacteria,  or  germs, 
and  the  decaying  matter  upon  which  they  live.  If  we 
take  bacteria  of  certain  diseases,  such  as  typhoid  fever 

and  cholera,  in  our 
drinking  water,  we 
may  "  catch  "  those 
diseases.  If  there  is 
any  chance  that  drink- 
ing water  may  be  im- 
pure, we  should  have 
it  tested.  We  cannot 
depend  upon  the  ap- 
pearance of  water,  for 

FIG.  87.  —  How    water    is    distilled.      The  J 

water  is  turned  into  steam  and  the  steam  passes  a  dirty  looking  Water 
through  a  "condenser"  surrounded  by  a  i  /.  •,  •  •. 

"jacket"    of    cold    water.     The    cold    water  m&y     ^      Sale,  Willie 

enters  at  the  bottom  of  the  jacket  and  over-  QQQ  ^g  dear  as  a 
flows  at  the  top.  Why? 

crystal    may    contain 

deadly  germs.  A  shallow  well,  either,  on  a  farm  or  in 
a  village,  is  always  to  be  thought  of  as  a  possible 
danger,  for  surface  filth  may  be  washed  into  it  by  rain. 
Besides,  kitchen  drains,  outbuildings,  and  barns  may  be 
near  enough  to  pollute  it.  Ice  made  from  filthy  water 
is  also  dangerous,  for  the  disease  germs  are  not  killed  by 
freezing,  but  are  only  made  inactive.  They  become 
active  again  as  soon  as  they  get  into  food  and  when  we 
take  them  into  our  bodies. 


WATER  SUPPLY  AND  SEWERAGE 


159 


138.  How  Can  We  Get  Pure  Drinking  Water  ?- 
When  the  chemist  wants  pure  water,  he  distils  it  (Fig.  87). 
We  can  get  pure  drinking  water  in  the  same  way.  The 
impurities  are  left  behind.  In  the  household  it  is  easier 
to  boil  water  than  to  distil  it.  Boiling  kills  the  germs, 
but  leaves  much  of  the  dissolved  materials  in  the  water. 

Do  you  like  the  flavor  of  distilled  or 
boiled  water  ?  Its  flat  taste  is  due  largely 
to  the  absence  of  the  gases  that  are 
present  in  natural  waters.  We  can  im- 
prove the  taste  by  shaking  the  water  in 
a  bottle  with  some  air,  or  by  pouring  the 
water  several  times  in  a  small  stream 
from  one  vessel  to  another.  Another  way 
is  to  filter  it  through  porous  stones.  In 
these  ways  the  water  may  be  made  to 
dissolve  some  of  the  air  it  lost  when  it 
was  distilled  or  boiled,  and  it  will  then 
have  a  better  taste.  Many  people  use 
a  filter  to  purify  water. 


; \ 


FIG.  88. —  Figures  1,  2,  3, 
and  4,  on  the  left,  show  how 
a  circular  piece  of  filter  paper 
must  be  folded,  so  that  it  will 
form  a  cone  that  will  fit  nicely 
into  the  funnel. 

139.  What  is  a  Filter  ?  —  A  filter  is  a  screen  with  very 
small  openings  so  that  only  liquids  and  dissolved  sub- 
stances can  pass  through  (Fig.  88).  In  household  filters 
gravel,  charcoal,  and  porous  stone  may  be  used  as  filter- 
ing materials.  These  strain  out  the  impurities  which 
are  floating  in  the  water,  including  the  bacteria.  Small 
porous-stone  filters  may  be  attached  to  faucets.  The  water 
runs  through  from  the  outside  to  the  inside  of  the  filter,  and 
the  dirt  collects  on  the  outside  where  it  may  be  removed 
easily.  If  a  filter  is  not  cleaned  often,  it  becomes  clogged 
with  dirt  and  bacteria  and  is  worse  than  no  filter  at  all. 


160  JUNIOR  SCIENCE 

140.  Can  a  City  Filter  Its  Water  ?  —  How  do  you  sup- 
pose a  city  filters  its  water?     City  filter  systems  are 
made  of  beds  of  sand;  these  are  often  acres  in  extent. 
Sand  is  loose  and  contains  much  air.     The  oxygen  of 
the  air  (cf .  §  34)  can  thus  penetrate  far  into  it  and  destroy 
the  bacteria  of  disease.     After  soaking  through  the  sand, 
the  water   enters  reservoirs   from   which  it  is  pumped 
through  the  water  "  mains  "  into  the  houses.     But  the 
large  filters,  like  the  small  ones,  must  be  emptied  some- 
times and  allowed  to  lie  idle,  so  that  the  sand  may  be 
purified  by  sunlight  and  air. 

141.  May  Water  be  Purified  by  Chemicals  ?  — The 
bacteria  of  disease  that  are  present  in  water  may  be 
destroyed  by  means  of  certain  chemicals.     One  of  these 
is  chloride  of  lime,  or  "  bleaching  powder."     This  is  a 
white  solid  that  can  be  bought  in  metal  cans.     A  certain 
amount  of  it  when  put  into  the  city's  water  supply  will 
make  the  water  fit  to  drink,  but  it  may  give  the  water  a 
slight   taste.     You   can  make   a  purifying   solution  for 
your  own  water  supply,  if  you  wish,  in  the  following  way  : 

Rub  an  even  teaspoonful  of  chloride  of  lime  with  a  little  water  until 
all  the  lumps  are  broken  up  and  you  get  a  smooth  paste.  Then  mi^ 
the  paste  with  four  cupfuls  of  water.  Put  this  solution  into  a  bottle, 
stopper  it  tightly,  and  let  it  settle.  To  purify  two  gallons  of  water, 
add  a  teaspoonful  of  the  clear  chloride  of  lime  solution,  stir  up  the 
water,  and  let  it  stand  for  ten  minutes. 

142.  What  is  Hard  Water?  —  We  often  hear  water 
spoken  of  as  "  hard/'  or  as  "  soft,"  water.     If  you  live 
in  a  village  or  in  the  country,  you  have  probably  noticed 
that  water  from  a  cistern  is  often  used  for  washing  pur- 


WATER  SUPPLY  AND  SEWERAGE 


161 


poses,  while  water  from  the  faucet  or  well  is  used  for 
drinking  purposes.  Cistern  water  is  very  likely  to  be 
impure,  in  that  it  contains  many  bacteria,  and  it  may, 
therefore,  be  unfit  to  drink.  Why  is  it  better,  then, 
for  washing?  When  soap  is  used  in  the  soft  rain  water 
of  the  cistern,  a  lather,  or  suds,  is  quickly  and  easily 
formed,  but  the  soap  lathers  with  great  difficulty  in  the 
hard  water.  Rain  water  is  always  soft.  Since  well 
and  spring  waters  were  once  rain 
water,  they  must  have  become  hard 
in  their  passage  through  the  ground. 
In  seeping  through  rock  and  ground 
layers,  the  water  dissolves  some  sub- 
stances which  make  it  hard.  Some 
of  these  substances  are  made  in- 
soluble when  the  water  is  boiled 
and  come  out  as  "  scale  "  (Fig.  89) ; 
others  must  be  forced  out  by  means 
of  some  chemical,  such  as  ammonia.  Ask  your  mother 
what  substances  besides  ammonia  are  used  to  make  water 
soft.  Does  soap  soften  hard  water? 

143.  Exercises. —  1.  Is  your  city  water  hard  or  soft?  Does  the 
inside  of  your  teakettle  have  a  scaly  deposit?  Where  does  it  come 
from?  What  is  the  source  of  your  water  supply?  Put  a  clean  pebble 
into  your  teakettle  and  leave  it  there  for  some  weeks.  Examine  it 
from  time  to  time  to  see  if  it  increases  in  size. 

2.  What  is  the  danger  in  drinking  surface  water? 

3.  What  are  the  dangers  in  camping?    How  may  they  be  over- 
come? 

4.  What  are  the  ways  of  purifying  water? 

5.  Why  is  it  necessary  to  clean  a  filter  frequently? 


FIG.  89.  —  How  the 
"hardness"  of  water  is  de- 
posited on  the  inside  of  a 
teakettle. 


162  JUNIOR  SCIENCE 

6.  What  is  the  value  of  a  "  trap  "? 

7.  Make  a  definition  for  distillation. 

8.  Find  out  what  industries  in  your  city,  or  the  city  nearest  you, 
need  a  large  supply  of  water  and  why. 

9.  Find  out  from  the  water  department  of  your  city  how  many 
gallons  of  water  the  city  uses  in  a  year.     What  is  the  population  of 
your  city?    How  much  is  its  per  capita  consumption  of  water? 


CHAPTER  XVI 


ROCKS    AND     SOIL 

144.  What  is  the  Earth's  Crust?  — What  do  you 
suppose  the  inside  of  the  earth  would  look  like,  if  we  could 
cut  it  through  its  center  into  two  great  halves?  This 
is  something  men  have  often  wondered  about.  In  such 
a  cutting,  or  cross  section  (Fig. 
90),  there  would  be  at  least  four 
different  layers  to  think  of.  First, 
there  is  the  atmosphere,  or  gas 
layer ;  then  there  is  the  water 
layer  that  covers  about  f  of  the 
earth  ;  the  third  is  the  land  layer, 
or  crust,  upon  which  we  live; 
the  fourth  is  the  inside,  or  core. 

In  this  chapter  we  consider  the 
third  layer  :  the  crust.  You  may 
have  heard  people  say :  "  Now 
we  are  at  the  bed  rock  of  the 
argument/ J  What  did  they  mean 
by  this  ?  They  meant  that  they  were  through  with  all  the 
little,  outside  reasons  and  had  reached  the  most  im- 
portant of  all.  In  the  earth's  crust  there  are  two  layers : 
the  mantle  rock  and  the  bed  rock.  The  mantle  rock  is 
the  loose,  outer  covering  of  soil,  sand,  clay,  gravel,  and 

163 


FIG.  90.  —  This  gives  us  an 
idea  how  a  cross  section  of  the 
earth  would  look.  Of  course, 
the  outer  layers  are  not  nearly 
so  thick  as  the  figure  shows 
them. 


164 


JUNIOR  SCIENCE 


pebbles.  This  may  usually  be  worked  without  much 
difficulty.  But  the  bed  rock  underneath  is  firm,  hard, 
and  difficult  to  cut  through.  A  railroad  cut  or  a  road 
cut  is  sometimes  deep  enough  to  cut  through  the  mantle 
rock  into  the  bed  rock.  Mantle  rock  is  much  thinner  at 
some  places  than  others ;  in  fact  the  bed  rock  sometimes 
comes  to  the  surface  and  we  have  an  outcrop.  Have  you 

ever  seen  a  river  which  has 
cut  down  to  bed  rock  ? 

145.  What  are  the  Classes 
of  Rocks  ?  -  -  Examine  a 
piece  of  soft  coal  and  note 
that  a  cross  section  of  the 
coal  is  marked  by  a  multi- 
tude of  parallel  lines,  be- 
cause the  coal  is  made  of 
thin  layers.  Limestone  looks 
much  the  same.  Such  rocks 
are  called  stratified,  or  "  made 
in  layers/7  One  layer  of 
material  seems  to  have  been 
spread  evenly  over  another,  just  as  one  leaf  of  a  book 
is  laid  upon  another. 

The  rocks  into  which  Niagara  Falls  (Fig.  91)  has  cut  are  good  ex- 
amples of  stratified  rocks.  The  rock  under  the  Niagara  River  is  a 
hard  limestone.  This  covers  a  soft  shale  layer  and  farther  down  we 
find  some  sandstone  layers.  Limestone,  sandstone,  and  shale  are 
stratified  rocks. 

Some  rocks  are  not  composed  of  layers.  They  are 
formed  of  crystallized  masses  which  are  interlaced  and 


Shale 


FIG.  91.  —  A  cross  section  of  the 
rock  layers  under  the  Niagara  Falls. 
Note  how  the  layers  of  hard  rock  are 
being  undermined  by  the  wearing  away 
of  the  soft  rocks.  (After  Gilbert.) 


ROCKS  AND  SOIL  165 

pressed  tightly  together.  These  are  unstratified  rocks. 
Granite,  lava,  and  pumice  are  good  examples  of  un- 
stratified rocks. 

Marble  is  believed  to  be  a  stratified  rock  which  has 
been  changed  by  heat  and  pressure,  until  it  has  the 
appearance  of  an  unstratified  rock. 

146.  How  Are  Stratified  Rocks  Formed  ?  —  How  are 
these  great  layers  of  hard  rock  formed  one  above  the 
other  ?     When  a  stream  empties  into  a  pond,  it  drops  its 
load  of  sand  and  dirt  and  this,  settling  to  the  bottom, 
forms  a  cover  over  the  whole  pond  floor.     A  rain  comes, 
enlarging  the  stream,  and  a  considerable  amount  of  dirt 
is  deposited.     The  larger  pieces  fall  first  and  then  the 
fine  dirt.     Later  another  rain  does  the  same  thing.     The 
large  particles  again  fall  first  and  are  covered  with  the 
finer  ones.     This  makes  the  fine,  parallel  lines  found  in 
the  stratified  rocks,  one  line  for  each  flood  time.     Sup- 
pose this  happened,  not  simply  in  a  pond,  but  in  a  river, 
a  lake,  or  the  sea,  and  happened  a  great  many  times, 
until  there  was  a  very  thick  deposit ;  the  lower  layers 
would  be  pressed  down  by  the  weight  of  those  above  and 
would   become   very   dense   and   compact.     Then,   if   a 
cementing  material  were  present,   the  clay  deposits  in 
the  pond  would  be  changed  to  shale,  the  sand  deposits 
to  sandstone. 

147.  What  are  Fossils  ?  —  When  we  break  apart  a 
mass  of  stratified  rock,  we  often  find  a  strange  figure : 
something  that  looks  exactly  like  a  leaf  with  its  stem 
and  delicate  veining   (Fig.   92).     Have  you  ever  found 
one?     It  is  as  though  the  leaf  had  "  turned  to  stone, " 


166 


JUNIOR  SCIENCE 


or  petrified.  Sometimes  we  find  a  piece  of  stem,  with 
the  scars  of  leaves,  or  a  piece  of  a  tree's  trunk,  with  the 
"  rings  of  growth  "  of  the  wood.  We  may  even  find  the 
seeds  and  fruit,  all  petrified.  Often  we  find  the  im- 
prints of  animals  ;  creatures  with  shells  looking  like  those 
of  snails  and  clams.  In  some  rocks  the  imprints  are 


(Copyright  by  Mclntosh  Slereoplicon  Co.) 
'      FIG.  92.  —  A  fossil  of  the  long  ago. 

those  of  fishes,  turtles,  and  lizards,  and  of  strange  insects 
and  birds.  All  these  marks  are  called  fossils.  We  may 
define  a  fossil  as  the  evidence  of  some  former  plant  or 
animal.  How  could  fossils  be  formed  in  rock,  far  below 
the  earth's  surface? 

To  explain  how  fossils  might  be  made  we  must  again  picture  to 
ourselves  how  stratified  rocks  are  formed.  Then,  as  now,  leaves,  or 
whole  trees,  fell  into  the  water  and  were  covered  with  mud  and  sand. 
Sometimes  dead  fishes,  snails,  birds,  or  insects  sank  into  the  stream 


ROCKS  AND  SOIL  167 

and  were  buried.  When  the  mud  and  sand  hardened  to  rock,  the 
impression  of  the  creature  remained  to  tell  us,  many  centuries  after- 
ward, of  the  life  that  was  once  upon  our  earth. 

148.  How  Are  Unstratified  Rocks  Formed  ?  —  While 
we  can  go  to  a  pond  and  by  careful  investigation  find 
out  how  stratified  rocks  are  formed,  it  is  not  so  easy  to 
find  unstratified  rocks  in  the  making.     Some  volcanoes 
in  action  throw  out  rivers  of  molten  rock ;  these  cool  to 
a  glassy,  brittle  rock  which  we  call  lava.     Sometimes  the 
mass  of  lava  is  full  of  gas  bubbles  and  cools  to  form  our 
porous  pumice.     Sometimes  the  lava  flows  up  into  cracks 
in  the  earth  and  hardens  in  large  crystals.     Granite  is  a 
volcanic  rock  that  has  cooled  slowly,  under  great  pressure, 
as  it  would  far  under  the  earth's  surface.     When  strati- 
fied rocks  are  heated  by  the  molten  rock  near  them, 
they  are  altered.     Thus  a  layer  of  limestone  might  be 
changed  to  marble. 

149.  What  is  Weathering  ?  —  Did  you  ever  think  how 
untiring  and  how  unceasing  in  her  labors  nature  is  ?     By 
the  long,  gradual  process  which  we  have  just  been  study- 
ing, nature  builds  her  rocks  ;  now  we  shall  learn  how  busy 
she  is  tearing  down  those  rocks  already  made,  at  the 
same  time  that  she  is  building  up  new  rocks.     The  process 
by  which  rocks  are  broken  down  to  form  sand,  clay,  soil, 
and  such  small  particles,  is  called  weathering,  or  erosion, 
or  "  wearing  away."    Weathering  is  made  possible  by  the 
combined  work  of  wind,  water,  ice,  plant  life,  and  heat. 

150.  How  Do  Plants  Cause  Weathering?  —  We  know 
that  plants  grow  in  soil,  but  did  3^ou  ever  think  that 
plants  can  make  soil  out  of  rock?     This  is  true  even  of 


168 


JUNIOR  SCIENCE 


such  tiny  plants  as  molds,  fungi,  and  bacteria.  Many 
of  these  are  far  too  small  to  be  seen  without  a  microscope. 
They  grow  in  the  ground  and  break  it  up  into  fine  par- 
ticles. They  even  take  materials  from  hard  rocks  and 
cause  the  rocks  to  crumble.  Not  only  do  the  living  plants 
act  upon  rock,  but  when  they  decay  they  produce  acids 
(cf.  §  175)  and  other  compounds  which  attack  the  rock. 


'•i 


(From  Hopkins'  Physical  Geography.) 
FIG.  93.  —  How  a  tree  may  help  in  breaking  up  rocks. 

While  these  small  plants  aid  in  making  the  soil  fine  and 
powdery,  large  plants  aid  by  pushing  their  roots  down 
into  cracks  in  the  rocks ;  thus  they  split  rocks  and  force 
them  apart  (Fig.  93).  Have  you  ever  seen  an  old  cement 
or  brick  sidewalk  which  has  been  broken  by  the  growing 
roots  of  a  tree  under  it  ? 

How  Do  Plants  Hinder  Weathering?  —  Plant  life  has  one  way  of 

defeating,  or  holding  back,  erosion.  If  you  have-  a  terrace  in  your 
yard,  you  have  seen  that  grass  seed  is  carefully  sowed  there  until  a 


ROCKS  AND  SOIL 


169 


firm  sod  results.  If  there  isn't  a  firm  sod,  the  water  that  runs  off  will 
cut  the  terrace  and  wash  parts  of  it  away.  The  sod  prevents  this  by 
holding  the  ground  and  keeping  a  smooth,  regular  surface.  How  does 
the  grass  hold  the  dirt  ?  .  Great  forests  act  in  the  same  way  on  a  hill- 
side. Conservation  of  the  forests  is  thus  very  important.  The  great 


(Courtesy  of  A.  M .  Lythgoe,  Metropolitan  Museum  of  Art,  New  York  City.) 

FIG.  94.  —  The  tiny  particles  of  desert  sand,  blown  by  the  winds  of  centuries, 
wear  away  the  hardest  rock. 

floods  of  China  are  said  to  be  partly  due  to  the  cutting  away  of  her 
forests.     Why? 

151.  How  Does  the  Air  Aid  Weathering?  —  Even  the 
invisible  air  helps  to  destroy  rocks,  for  it  furnishes  oxygen 
which  unites  with  rock  substances  to  soften  and  break 
them  up.  What  happens  to  a  piece  of  iron  if  it  is  left 
out  of  doors  for  some  time?  We  say  it  rusts;  that  is, 


170  JUNIOR  SCIENCE 

it  unites  with  oxygen  from  the  air  and  forms  iron  oxide, 
which  is  the  red  powder,  rust.  In  the  same  way  other 
hard,  firm  substances  are  changed  to  fine  particles  after 
uniting  with  oxygen.  The  carbon  dioxide  in  the  air 
unites  with  water  and  forms  an  acid  (carbonic  acid) ; 
this  breaks  up  certain  rocks. 

Air  in  motion,  as  wind,  assists  in  erosion,  especially  in  dry  climates 
and  desert  regions.  Great  windstorms  carry  fine,  loose  particles  of 
sand  and  throw  them  violently  against  any  object,  rock,  or  plant 
which  the  wind  passes  over.  Huge  mounds  of  sand  are  moved  by 
the  wind,  and  each  grain  hitting  a  rock  surface  chips  it  a  little.  The 
great  stone  monuments  which  were  built  in  Egypt  thousands  of  years 
ago  show  well  the  power  of  the  wind  and  sand  to  break  off  a  great  deal 
of  stone  if  given  time  enough  (Fig.  94). 

152.  How  Do  Water  and  Ice  Cause  Weathering  ?- 
The  water  of  streams,  lakes,  and  oceans  aids  in  the 
weathering  of  rocks  in  ways  which  we  have  already 
studied.  Frost  and  ice  are  powerful  agents  in  breaking 
up  rocks.  If  you  leave  water  in  your  pipes  on  a  cold 
winter's  night,  and  do  not  have  a  fire  in  the  house,  the 
next  morning  you  may  find  that  one  of  the  pipes  has 
frozen  and  burst.  Why  does  it  burst  ? 

Perform  this  experiment :  Fill  an  old  medicine  bottle  entirely  full 
of  water  and  stopper  it  tightly.  Leave  it  outside  on  a  freezing  night. 
The  next  morning  you  will  probably  find  that  the  stopper  has  either 
been  forced  out,  or  the  bottle  is  broken.  Water  expands  when  it 
freezes  (cf.  §  124).  In  the  same  way  water  seeps  into  cracks  and 
joints  in  the  rocks;  there  it  freezes,  expands,  and  forces  even  great 
rocks  apart.  After  a  cold  winter  in  which  there  has  been  a  great 
deal  of  freezing  weather,  chips  of  rock  and  even  large  slabs  are  found 
at  the  foot  of  cliffs.  These  are  forced  off  by  the  ice  and  frost. 


ROCKS  AND  SOIL  171 

Great  sheets  of  ice  assisted  erosion  in  past  ages,  and 
ice  streams  (glaciers)  are  at  work  in  the  mountains  now. 
An  immense  ice  sheet  once  covered  the  Great  Lakes  region 
of  the  United  States.  Huge  deposits  of  mud  and  rock 
(Fig.  95)  were  left  after  the  melting  of  the  ice.  With  the 


(From  Hopkins'  Physical  Geography.) 
FIG.  95.  —  Rocks  brought  by  the  great  ice  sheets  and  left  when  the  ice  melted. 

rocks  frozen  in  its  under  side,  the  ice  sheet  was  able  to 
scour  and  scrape  out  lakes  and  to  grind  surface  rocks  to 
powder. 

153.  How  Is  Our  Soil  Formed? — Did  you  ever 
wonder  how  "  hard  heads/7  or  granite  bowlders,  came  to 
our  fields,  when  the  bed  rock  below  may  not  be  granite 
at  all?  Is  it  possible  that  the  soil  of  our  gardens  was 


172  JUNIOR  SCIENCE 

not  always  where  we  find  it,  but  was  brought  from  other 
regions?  There  are  two  ways  in  which  soil  is  formed  on 
any  particular  spot.  First,  we  have  the  soil  which  was 
formed  from  the  rocks  beneath  it  by  the  weathering  of 
those  rocks.  It  is  composed  of  the  same  substance  as 
the  rocks  below.  The  only  difference  we  find  in  the 
character  of  such  soil  as  we  dig  down  is  that  the  particles 
become  larger  all  the  time,  until  we  strike  bed  rock. 

The  other  class  of  soil  is  that  which  is  brought,  or  deposited  there, 
from  a  distance.  Glacial  soil  belongs  to  this  class ;  it  is  that  brought 
by  glaciers  and  spread  over  immense  areas ;  these  may  have  a  totally 
different  sort  of  bed  rock.  Another  soil  is  formed  on  the  slopes  of 
hillsides  or  mountains.  The  action  of  gravity  and  of  the  rain  causes 
great  masses  of  it  to  move  slowly  down  into  the  valleys.  Alluvial 
soil  is  formed  by  the  deposits  of  lakes  and  streams.  A  fourth  kind  of 
soil  is  fine  and  loose  and  deposited  by  the  wind.  It  is  found  chiefly 
in  desert  regions.  In  general,  the  transported  soils  are  made  up  of 
particles  weathered  from  rocks  of  many  kinds  and  are  a  richer  com- 
bination for  the  growing  of  crops  than  the  soils  which  were  formed 
where  we  find  them.  Why? 

154.  What  is  the  Structure  of  Soil?  —  We  can  see, 
as  we  look  at  it  carefully,  that  soil  is  made  up  of  particles 
of  different  sizes.  We  call  them,  according  to  size, 
gravel,  sand,  silt,  and  clay.  Which  has  the  smallest 
particles?  Usually  there  is  also  decayed  vegetable 
matter,  or  humus.  Each  tiny  particle  is  surrounded  by 
a  film,  or  covering,  of  water.  Water  is  also  held  be- 
tween the  particles  by  capillary  action  (cf.  §  108),  so 
that  the  plant  can  draw  moisture  from  deep  down  in  the 
ground,  even  in  dry  weather.  The  water  holds  in  solu- 
tion those  substances  which  are  needed  by  the  plant  and 


ROCKS  AND  SOIL  173 

which  must  be  taken  from  the  ground.  Thus  water  is 
absolutely  necessary  to  the  life  of  the  plant.  %  Plants  die 
if  their  leaves  are  not  in  the  air,  so  that  they  can  breathe ; 
there  must  be  air  in  the  soil,  too,  so  that  the  roots  also 
can  breathe.  A  soil  that  is  very  solid  and  airless  chokes 
the  roots  so  that  the  health  of  the  plant  suffers. 

155.  Why  Must  Soil  Be  Tilled?  — Did  you  ever  notice 
how  much  labor  a  farmer  or  gardener  spends  in  stirring 
up,  or  tilling,  the  soil  in  which  he  plants  his  seeds?     Soil 
is  tilled  so  as  to  improve  its  structure,  in  order  that  it 
may  hold  air  and  water  better  and  may  permit  the  roots 
to  gather  the  plant's  food  from  larger  amounts  of  ground. 
Tillage   also   turns   under   rubbish,   manure,    and   other 
fertilizers,  so  that  they  become  a  part  of  the  soil  and 
enrich  it. 

In  ancient  times  men  had  very  few  tools,  or  implements,  to  help 
them  in  tilling  the  soil,  but  the  modern  farmer  has  many  of  them.  A 
plow  is  really  a  slanting  knife,  or  shovel,  that  is  forced  into  the  ground, 
so  that  it  turns  a  slice  of  soil  over.  Cultivating  is  shallow  plowing; 
it  stirs  up  the  top  layer  of  the  ground,  so  that  it  is  in  a  powdery  con- 
dition. Disk  plows  have  a  revolving  cutting  instrument  called  a  disk, 
instead  of  a  knife  plowshare.  A  gang  plow  consists  of  many  plow- 
shares or  disks  attached  to  one  frame.  It  is  drawn  by  many  horses 
or  by  an  engine,  or  tractor  (Fip:.  96). 

156.  What  is  Irrigation?  —  If  you  go  to  the  Far  West 
you  will  be  shown  great  mountains,  canons,  and  cataracts 
as  its  wonders ;  but  these  are  not  the  only  great  wonders 
of  the  west.     As  great  a  marvel  as  any  is  the  transforma- 
tion of  land  once  a  desert  waste  into  fertile  orchards  and 
farms.     How  has  this  apparent  miracle   come  about? 


174 


JUNIOR  SCIENCE 


In  dry,  desert  areas  plants  and  crops  cannot  grow  unless 
the  soil  receives  more  water  than  is  given  to  it  by  the 
rain.  Even  in  almost  rainless  regions  there  is  usually 
a  lake  or  stream  that  has  a  large  amount  of  water  during 
the  rainy  season,  or  in  the  spring,  when  the  mountain 
snow  melts.  But  in  the  summer  there  is  no  water.  To 
even  up  the  water  supply  large  reservoirs  are  built  and 


(Courtesy  of  Deere  &  Co.) 
FIG.  96.  —  How  machinery  makes  it  possible  for  men  to  farm  on  a  large  scale. 

filled  by  damming  up  lakes  or  streams.  These  reservoirs 
hold  the  water  of  the  rainy  season  for  use  during  the 
summer.  Irrigation  canals  carry  water  from  the  reser- 
voirs to  the  farms. 

157.  Do  Crops  Rob  the  Soil?  — When  we  speak  of 
the  fertility  of  the  soil,  we  mean  its  crop-producing  power. 
This  power  depends  upon  the  elements  contained  in  the 
soil,  the  structure  of  the  soil,  and  the  water  supply. 
However,  a  perfect  soil  for  a  certain  plant  cannot  produce 


ROCKS  AND  SOIL  175 

that  plant  if  the  climate  is  unfavorable.  A  soil  which 
produces  oranges  in  Florida  could  not  produce  them  in 
Illinois.  About  ten  elements  are  necessary  for  plant 
life.  They  are:  carbon,  hydrogen,  oxygen,  nitrogen, 
phosphorus,  potassium,  calcium,  sulphur,  magnesium, 
and  iron.  Which  of  these  come  in  part  from  the  air? 

Fertility  is  lost  by  the  growing  of  plants  because  the  plants  need 
to  take  certain  elements  from  the  soil.  If,  then,  we  remove  or  harvest 
the  plant,  the  ground  gets  nothing  in  return.  This  loss  of  fertility 
cannot  be  avoided.  However,  soil  loses  fertility  in  some  ways  which 
can  be  avoided.  Thus,  improper  draining  on  sloping  land  allows  rains 
to  wash  away  valuable  materials.  Then,  too,  if  certain  crops  are 
grown  too  long  upon  a  piece  of  land,  its  soil  becomes  acid,  or  sour, 
and  thus  loses  fertility. 

158.  How  Can  Soil  be  Kept  Fertile  ?  —  While  we  cannot 
help  removing  fertility  when  we  remove  a  crop,  yet  the 
loss  can  be  restored.  We  must  put  everything  back  on 
the  land  that  is  not  actually  sold  or  used.  That  is  why 
the  farmer  uses  manure,  the  most  common  of  fertilizers ; 
it  restores  plant  food  to  the  soil.  The  farmer  does  not 
profit  if  he  sells  the  fertility  of  his  soil  at  too  low  a  price. 
Thus,  when  grains  are  cheap,  it  may  be  most  profitable 
to  use  them  as  cattle  food,  because  the  price  received  for 
farm  fertility  as  meat  is  often  greater  than  that  received 
for  it  as  grain.  Besides,  when  cattle  are  raised,  much 
of  the  farm's  fertility  can  be  restored  as  manure. 

Dairying  is  profitable,  because  dairy  products  (What 
are  they?)  bring  a  good  price,  and  because  they  do  not 
remove  much  fertility.  If  we  sell  butter,  for  example, 
we  are  selling  chiefly  fat.  Now,  fat  is  composed  of 


176  JUNIOR  SCIENCE 

carbon,  oxygen,  and  hydrogen  (cf.  §  189),  which  are 
elements  coming  from  water  and  from  the  carbon  dioxide 
of  the  air.  If  the  skim  milk  is  used  on  the  farm,  the  soil 
need  not  lose  its  fertility. 

159.  Why  Should  Crops  Be  Rotated  ?  — Rotation,  or 
changing  of  crops,  on  a  certain  piece  of  land,  is  now  used 
by  all  good  farmers.     Different  crops  use  different  soil 
elements.     Corn  removes  much  of  all  three  of  the  ele- 
ments nitrogen,  phosphorus,  and  potassium,  and  should- 
not    be   planted    every   year.     Grains,    such   as .  wheat, 
which  take  up  phosphorus,  and  grass,  which  takes  up 
little  phosphorus,  are  often  grown  for  two  years  and  then 
corn  in  the  third  year. 

Rotation  is  good  in  other  ways,  for  roots  of  different 
plants  differ  from  one  another  and  one  plant  will  often 
break  up  the  ground  for  another.  The  diseases  and  pests 
of  plants  differ,  too,  and  one  plant  will  not  be  affected 
by  those  of  another. 

Have  you  seen  artificial  fertilizers  ?  They  are  usually 
powdered  substances  which  contain  the  elements,  or 
some  of  the  elements,  needed  to  give  back  to  the  soil 
what  has  been  taken  from  it  by  crops.  Fertilizers  are 
spread  over  the  ground,  or  "  plowed  under. "  Gener- 
ally they  supply  one  or  more  of  the  three  elements  :  phos- 
phorus, potassium,  and  nitrogen. 

160.  Exercises. —  1.   Make  definitions  for  these  terms:  fossil,  bed 
rock,  outcrop,  stratified  rock,  weathering,  soil,  glacier,  irrigation,  soil 
fertility. 

2.  Why  are  beach  pebbles  rounded? 

3.  Report  some  case  of  weathering  you  saw  on  the  way  to  school. 


ROCKS  AND  SOIL  177 

4.  Find  out  from  a  gardener  what  kind  of  soil  is  best  for  the  grow- 
ing of  potatoes. 

5.  Ask  a  florist  how  he  prepares  soil  for  the  growing  of  flowers. 

6.  Why  do  farmers  "  cultivate  "  the  soil  between  rows  of  corn? 

7.  Of  what  use  are  song  birds  to  the  farmer? 

8.  What  are  some  of  the  tools  and  implements  used  on  the  farm? 

9.  What  advantages  has  a  child  that  grows  up  on  the  farm? 
What  disadvantages? 

10.  Do  you  think  that  a  farmer  ought  to  burn  up  the  stubble  in 
his  fields,  or  let  it  rot  and  become  part  of  the  soil?     Find  out  the 
reasons. 

11.  Find  out  what  substances  are  in  skim  milk.     For  what  can 
skim  milk  be  used? 

12.  Bring  to  school  some  samples  of  stratified  and  of  unstratified 
rocks. 


CHAPTER  XVII 
MINERALS  AND   METALS 

161.  What  are  Minerals?  —  We  have  already  looked 
at  our  earth  as  made  up  of  several  layers :  the  air,  the 
water,  the  crust,  and  the  interior,  or  core ;  we  have  also 
looked  upon  it  as  made  up  of  elements  (cf.  §  113).  We 
may  now  look  upon  it  as  made  up  of  animal,  vegetable, 
and  mineral  material.  When  we  realize  that  rocks  are 
made  up  of  minerals,  we  can  understand  that  minerals 
make  up  much  more  of  the  earth  than  the  other  two  put 
together.  Some  of  these  minerals,  such  as  granite,  seem 
never  to  have  had  anything  to  do  with  life,  while  others, 
such  as  coal,  are  the  remains  of  former  living  things. 
Those  substances  which  are,  or  have  been,  part  of  a  living 
thing,  or  organism,  we  call  organic  substances.  Name 
some  of  them. 

Quartz,  clay,  sand,  flint,  chalk,  gold,  copper,  and  even 
water  are  minerals,  so  you  see  that  minerals  differ  greatly 
in  their  qualities.  Most  of  the  metals  are  found  united 
with  other  materials,  just  as  hydrogen  and  oxygen  are 
united  in  water.  Those  minerals  from  which  we  may  take 
out,  or  "  extract/7  a  metal  are  called  ores  of  that  metal. 
Most  of  our  common,  useful  metals  are  found  in  ores. 
Lead,  iron,  tin,  zinc,  silver,  gold,  and  copper  are  taken 
from  the  ground  as  ores,  although  gold  and  copper  are 
sometimes  found  in  nature  in  a  pure  form.  To  start 

178 


MINERALS  AND   METALS  179 

with  the  lead  ore  and  to  turn  out  a  lead  pipe  takes  a 
great  deal  of  time,  machinery,  and  labor.  Many  huge 
factories  all  over  our  country  are  working  to  get  the  useful 
metals  out  of  the  ores  in  which  nature  placed  them. 

162.  Is  Iron  Necessary  to  Man?  —  If  we  were  to  give 
up  everything  in  our  homes  or  in  the  food  we  eat  that  is 
made  of  iron  or  is  made  by  means  of  iron  machinery,  we 
should   have  practically   nothing  left.     Can   you   name 
anything  which  would  remain?     A  race  which  does  not 
use  iron  has  few  tools  and  conveniences  and  cannot  be 
highly  civilized.     Most  ancient  peoples  used  iron  to  some 
extent :     the  old  Egyptians  employed  it ;  it  is  found  in 
the  ruins  of  Babylon.     Could  our  modern  inventions, 
such  as  the  automobile,  telephone,  victrola,  and  steam 
engine,  exist  without  iron  ? 

163.  How  Is  Iron  Found?  —  The  commonest  ore  of 
iron,  which  furnishes  half  of  all  the  iron  used,  is  called 
hematite.     Hematite  is  a  compound  of  iron  and  oxygen, 
a  rough,   ordinary-looking  rock  varying  in   color  from 
gray  to  reddish  brown.     The  ore  is  often  in  great  ledges 
and  has  to  be  blasted  out.     Then  it  is  sent  to  the  smelters, 
or  furnaces,  to  be  smelted,  or  turned  into  metal.     The 
smelter  is  usually  built  near  some  industrial  center  that 
has  good  coal  within  easy  reach ;  for  coal  is  needed  to 
remove  the  oxygen  of  the  ore.     Much  of  the  iron  ore 
from  the  deposits  in  Minnesota,  Wisconsin,  and  Upper 
Michigan  is  sent  down  the  Great  Lakes  in  large  steamers. 
Did  you  ever  see  one? 

164.  How  Is  Iron  Prepared?  —  How  do  you  suppose 
early  man  learned  to  smelt  iron?     The  ancients  did  it 


180 


JUNIOR  SCIENCE 


in  a  very  primitive  manner.  They  built  fires  in  the  rocks 
in  such  a  way  that  there  was  a  strong  wind  blowing 
through  the  fire.  When  iron  ore  was  placed  in  the  fire, 
the  fuel  (wood  or  charcoal)  united  with  the  oxygen  of 
the  ore,  leaving  the  iron.  The  iron  metal  melted  and  ran 


(Copyright  &y  Mclntosh  Stereopttcon  Co.) 

FIG.  97.  —  In  a  blast  furnace  iron  ore,  coal,  or  coke,  and  limestone  are  heated 
together  to  produce  pig  iron  and  slag. 

to  the  bottom  of  the  fire,  while  the  dirt  and  stone  of  the 
ore  remained  with  the  ashes. 

There  have  been  many  improvements  upon  this  method,  until  we 
now  have  the  modern  blast  furnace  (Fig.  97).  The  blast  furnace  is 
about  100  feet  high  and  is  filled,  by  means  of  machinery,  with  coal 
or  coke,  iron  ore,  and  limestone.  Limestone  is  used  because  it  unites 
with  the  dirt  and  stone  of  the  ore  to  form  slag  and  thus  leaves  a  purer 


MINERALS   AND   METALS 


181 


iron.  A  strong  artificial  wind  (a  "  blast  "  of  hot  air)  enters  at  the 
bottom  of  the  furnace ;  the  whitehot  iron  runs  down  into  the  hearth, 
where  it  is  drawn  off  into  sand  troughs.  Why  is  sand  used? 


"  pig  iron/' 


The  iron  in  this  stage,  or  form,  is  called 
or  cast  iron.  This  pig  iron  still  contains  many  impuri- 
ties ;  they  are  removed  by  another  process,  until  wrought 
iron,  or  soft  iron,  is  ob- 
tained. Steel  is  a  most  ^^^ 
useful  form  of  iron,  hard 
and  durable,  yet  elastic. 
It  can  be  "  tempered, "  so 
that  it  becomes  very  hard 

and  can  be  sharpened  to    r     ^ ^-.-..-       --^ 

a  keen  edge,  as  in  cutting     {^fc^&^^l^^  ^'Iv^li* 
tools,  such  as  axes,  saws, 
knives,  and  razors. 

165.   How  Is  Lead  Ob- 
tained? —  Lead   is    ex- 


u!~ 


FIG.  98.  —  How  a  deposit  of  lead  ore 
might  look  in  the  ground.  The  black 
spots  represent  the  ore. 


tracted    from    galena,    a 

heavy,  gray  ore  (Fig.  98) 

which    is     a     compound 

of   lead   and   sulphur.     Galena   is   usually    smelted    by 

heating   it   with   iron.     The   sulphur   then   unites   with 

the  iron  and  the  free  lead  sinks  to  the  bottom  of  the 

furnace. 

Lead  is  used  in  pipes  for  plumbing,  in  storage  batteries, 
for  paints  (you  have  heard  painters  speak  of  "  white 
lead  "),  and  in  making  mixtures,  or  alloys,  with  other 
metals.  Some  of  these  alloys  are  solder,  pewter,  shot 
metal,  and  the  type  metals  used  in  printing. 


182  JUNIOR  SCIENCE 

166.  How  Is    Copper    Obtained  ?  — The    free    metal 
copper  is  found  in  the  regions  of  Lake  Superior ;  from 
these  it  was  obtained  by  some  of  the  Indians  before  the 
coming  of  the  white  man  and  was  used  for  the  making 
of  knives  and  other  implements.     The  greatest  copper 
mines  in  the  United  States  are  in  Michigan,  Montana, 
and  Arizona.     Where  the  copper  is  found  as  a  metal, 
the  smelting  of  its  ore  is  a  simple  process.     The  ore  is 
crushed  in  very  fine  pieces  and  the  copper  is  separated 
out  by  washing.     It  is  then  melted  and  run  into  molds. 

The  alloys  of  copper  are  very  important.  Brass  is  made  of  copper 
and  zinc.  Bronze  is  a  mixture  of  copper,  tin,  zinc,  and  lead.  German 
silver  is  copper,  zinc,  and  nickel.  Copper  and  aluminum  form  alu- 
minum bronze,  resembling  gold.  Can  you  name  some  of  the  uses 
of  these  alloys? 

167.  How  Are  Gold  and  Silver  Found?  —  Why  are 
gold  and  silver  precious?     They  are  beautiful  in  their 
soft,  pretty  sheen,  but  their  being  precious  is  due  largely 
to  the  fact  that  they  are  scarce.     Gold  is  not  found 
even  as  abundantly  as  silver  and  is,   therefore,   more 
precious  than   silver.     Because   of  its  attractive   color, 
gold  was  probably  the  first  metal  found  by  man. 

Much  gold  is  found  as  fine  grains  in  the  gravel  of 
streams.  This  was  once  in  rocks,  but  the  decay  of  the 
rocks  has  freed  the  gold.  Men  wash  gold  grains  out  of 
loose  soil  and  gravel  by  the  use  of  streams  of  water.  As 
the  water  containing  gold  is  passed  over  mercury,  even 
the  smallest  pieces  of  the  gold  are  dissolved  in  the 
mercury.  Later  the  mercury  is  distilled  off,  leaving 
the  gold. 


MINERALS  AND   METALS 


183 


In  early  days  gold  grains  were  washed  out  of  loose  soil  and  gravel 
by  the  use  of  water  in  a  pan  (Fig.  99).  As  the  water  was  stirred  up, 
the  lighter  particles  of  soil,  sand,  and  gravel  could  be  poured  off  with 
the  water,  while  the  gold,  which  was  heavier,  remained  in  the  bottom 
of  the  pan. 

What  is  the  meaning  of  the  expression :  "  How  is  this  going  to 
1  pan  out '?  "  What  is  "  pay  dirt  "? 


(Copyright  by  Mclntosh  Stereopllcon  Co.) 
FIG.  99.  —  Panning  river  gravel  for  the  heavy  grains  of  gold. 

Silver  is  often  found,  in  nature,  united  with  sulphur. 
The  fact  that  a  silver  spoon  turns  black  when  used  with 
an  egg  (which  contains  sulphur)  shows  how  readily  silver 
unites  with  sulphur. 

168.  What  is  22-Carat  Gold?  — Gold  and  silver  are 
both  too  soft  to  use  in  their  pure  state,  and  they  must 


184  JUNIOR  SCIENCE 

be  alloyed  (or  mixed)  with  a  hard  metal  to  make  them 
fit  for  use.  The  purity  of  gold  is  stated  in  carats.  Pure 
gold  is  "  24  carats  fine."  Jeweler's  gold  is  22  carats  fine. 
This  means  that  22  parts  of  it  are  pure  gold  and  2  parts 
are  alloy.  Ten-carat  gold  is  10  parts  gold  and  14  parts 
alloy.  Gold  is  usually  alloyed  with  silver  and  copper. 
Silver  is  alloyed  with  copper. 

169.  How    Do    Men   Find    Precious  Stones?  — The 

precious  stones,  such  as  diamonds,  rubies, 
sapphires,  and  emeralds,  are  found  loose 
in  earth  or  in  rocks.  When  found,  the 
stones  are  surrounded  by  rocky  material 
which  has  to  be  removed.  Then  the  stone 
FIG  is  "  cut/7  or  ground.  After  the  cutting, 

HOW  a  diamond   rays  of  light  can  pass  through  the  stone  at 

is  cut  so   as   to  T/V  i  T  i         •, 

give  it  many  many  dmerent  angles  and  make  it  more 
•'facets/'  or  sur-  beautiful.  Much  of  the  beauty  of  a  gem  lies 

faces,     for     the 

flashing  of  light,   in  the  skill  with  which  it  is  cut  (Fig.  100). 

The  precious  stones  are  among  the  hardest  substances  known  to 
man.  Indeed,  the  diamond,  which  is  the  most  precious  of  all,  is  the 
hardest  substance  in  nature.  The  greatest  number  of  diamonds,  and 
the  largest  of  them,  are  mined  in  South  Africa.  Sometimes  we  see 
a  diamond  which  has  a  flaw  in  it :  a  small,  dark  spot.  This  shows  the 
origin  of  the  stone.  The  brilliant,  flashing  diamond  is  only  a  pure 
form  of  common  carbon,  such  as  is  in  coal  or  charcoal.  But  it  is  carbon 
which  has  probably  been  heated  and  kept  for  years  under  intense 
pressure. 

Like  gold  and  silver,  our  precious  stones  are  precious  quite  as  much 
because  of  their  scarcity  as  because  of  their  beauty. 

170.  What  is  Coal?  —  When  you  sit  in  front  of  your 
grate  fire,  watching  the  flames  play  about  the  coal,  do  you 


MINERALS  AND   METALS 


185 


ever  wonder  how  we  happen  to  have  coal?  Yes,  you 
know  that  coal  is  mined,  or  taken  from  the  ground,  and 
brought  to  you ;  but  how  did  it  get  into  the  ground  ? 
It  is  not  like  the  other  rocks  of  the  earth's  crust.  Then 
what  is  it,  and  how 
did  it  get  between 
the  rock  layers  ? 
Thousands  of 
years  ago  great, 
luxuriant  forests 
grew  on  the  places 
where  we  now  find 
coal  fields.  They 
grew  up  and  lived 
and  died  and  fell  to 
the  marshy  ground 
on  which  they 
stood.  Others 
grew  up  in  their 
place ;  they,  too, 
fell  in  turn  into 
the  marshy  land 
and  were  covered 
by  water.  Some- 
times, probably,  the  land  was  lowered  and  the  former  forests 
were  under  water  and  covered  with  sediment  and  mud. 
This  sediment  afterwards  became  rock.  Some  of  the  gases 
escaped,  but  the  rest  of  the  carbon  of  the  plants  was  held 
under  the  great  pressure  of  the  layers  of  rock  and  water 
above  it,  until  it  gradually  hardened  to  form  coal  (Fig.  101). 


FIG.  101.  —  What  a  cross  section  of  a  coal  mine 
might  look  like.  Note  the  great  crack  across  the 
rock  layers  and  the  way  in  which  the  upper  part 
has  slipped  down,  producing  a  fault. 


186  JUNIOR  SCIENCE 

In  swampy  regions  we  can  see  soft  peat  being  formed  today. 
This  was  probably  the  first  form  of  soft,  or  bituminous,  coal. 
Hard  coal  is  also  called  anthracite ;  it  gives  off  much  less 
gas  than  soft  coal  (cf.  §  28)  and  so  is  harder  to  set  on  fire. 
Where  are  some  of  the  coal  fields  of  the  United  States? 
Did  you  ever  see  a  piece  of  coal  which  had  on  it  the  im- 
print of  the  leaf,  stem,  or  trunk  of  a  plant  or  tree  ? 

171.  What  are  Our  Building  Stones  ?  — Some  of  the 
stones  used  in  building  are  granite,  limestone,  sandstone, 
and  marble.     The  quarrying  of  stone  furnishes  employ- 
ment for  a  great  number  of  men  in  this  country.    Much 
granite  is  taken  from  New  Hampshire,   the   "  Granite 
State."     It  is  very  hard  and  will  sustain  a  great  weight. 
Limestone  and  sandstone  are  softer  rocks,  but  very  useful. 
When  limestone  is  heated,  carbon  dioxide  escapes  and 
lime    remains.     Lime    is    used    in    making    mortar    and 
plaster.     Limestone  is  also  used  in  the  smelting  of  iron 
(cf.   §  164).     Marble  is  perhaps  the  most  beautiful  of 
our  building  stones.     It  is  of  many  different  colors  and 
may  be  highly  polished.     How  does  marble  act  with  an 
acid?     Read  §38. 

172.  Does    Man   Ever   Make    Stones? --You   have 
heard  of  artificial  jewels,  but  have  you  ever  seen  artificial 
building  stones?     Of  course  you  have.     Man  has  not 
always  been  able  to  get,  or  been  satisfied  with,  natural 
stones,  so  he  has  made  certain  ones  for  himself.     Such 
are  bricks  and  concrete. 

Bricks  were  made  long  ago  in  Egypt,  Assyria,  and 
Babylonia,  and  they  are  made  in  great  quantities  even 
now  in  our  own  country.  Finely  powdered  clay  is  mixed 


MINERALS  AND  METALS  187 

with  water  and  the  mixture  is  either  packed  into  molds 
or  is  cut  into  bricks  by  machinery.  The  bricks  are  then 
dried  in  the  air  for  several  days  and  later  baked  in  im- 
mense ovens  for  several  more  days. 

Mortar,  used  to  fasten  bricks  together,  sets  or  hardens 
to  form  another  artificial  stone. 

Concrete  is  more  durable  even  than  brick.  Men  make 
it  by  mixing  crushed  stone,  sand,  and  cement.  Then 
they  put  it  into  molds  and  keep  it  from  drying  too  rapidly 
by  covering  it.  You  have  seen  freshly-made  concrete 
sidewalks  covered  with  boards,  or  cloths,  until  the  con- 
crete has  "  set/'  or  hardened.  It  hardens  better  if 
sprinkled  with  water  occasionally.  Concrete  is  used 
not  only  for  sidewalks  and  floors,  but  for  the  foundations 
and  walls  of  buildings,  for  bridges,  and  even  for  ships ! 

173.  Exercises. —  1.  Why  are  layers  of  limestone  and  sandstone 
often  found  between  layers  of  coal? 

2.  Is  petroleum  a  mineral?     Where  is  it  found?     For  what  is  it 
used? 

3.  Why  is  iron  ore  shipped  from  the  Lake  Superior  region  to  Penn- 
sylvania to  be  smelted? 

4.  Name  five  or  more  great  uses  of  some  form  of  iron. 

5.  Why  do  we  believe  that  coal  is  made  up  of  the  material  of 
ancient  forests? 

6.  What  metals  are  called  "  precious  "  metals?    What  are  the 
"  base  "  metals? 

7.  Find  out  the  value  of  the  silver  in  a  silver  dollar. 

8.  What  is  solder  used  for?     Pewter? 

9.  Why  is  iron  often  coveted  (plated)  with  tin?     With  a  magnet 
test  a  pin  and  then  a  needle.     Is  either  made  of  a  form  of  iron? 


PART  IV 
SCIENCE   IN   THE   HOUSEHOLD 


CHAPTER  XVIII 
ACIDS  AND  ALKALIES 

174.  Do  We  Use  Science  in  the  Home  ?  —  Have  you 
ever  thought  how  strange  it  is  that  men  have  learned  to 
gather  and  to  prepare  so  many  different  substances  and 
to  use  each  of  them  for  some  special  purpose  ?     Just  think 
what  a  collection  of  substances  there  is  in  a  druggist's 
shop.     The  modern  housewife  has  not  nearly  so  many 
as  the  druggist,  yet  she  has  a  long  list.     Here  are  some 
of  them :     baking  soda,  washing  soda,  chloride  of  lime, 
lye,  bluing,  borax,  starch,  cream  of  tartar,  salt,  ammonia 
water,  vinegar,  sugar,  flour,  lard,  baking  powder,  soap, 
ink,  to  say  nothing  of  milk,  butter,  and  our  other  foods. 
It  is  out  of  these  materials  that  our  meals  are  made  ready 
for  the  table,  our  laundry  work  is  done,  our  letters  are 
written,  our  stains  are  erased.     Can  you  name  any  other 
household  substances? 

175.  Where  Are  Acids  Found  ?  —  As  you  know  very 
well,  we  use  vinegar  to  make  certain  articles  of  food  sour, 
or  "  acid."     This  is  true  of  beets,  pickles,  and  salads. 
The  chemist  says  that  vinegar  is  sour  because  it  contains 
an  acid:   acetic  (pronounced  a-set'Ic)  acid.     Most  acids 
have  a  sour  taste. 

Vinegar  is  the  result  of  a  fermentation,  or  change 
caused  by  a  ferment  (Fig.  102).  Ferments  are  found  in 
small  organisms  that  exist  in  nature  and  in  some  way  or 

191 


192 


JUNIOR  SCIENCE 


Fermented  Fruitjuices 
(dilute  alcohol) 


other  get  into  our  fruit  juices  and  other  food  materials. 
In  the  fall  you  may  have  seen  how  a  cider  press  extracts 
the  juice  of  apples  and  so  makes  "  sweet  cider."  If  we 
try  to  keep  sweet  cider  very  long,  it  bubbles  and  becomes 
"  hard."  The  bubbling  is  due  to  the  escape  of  carbon 
dioxide;  the  "  hardness  "  is  due  to  alcohol.  The  reason 

for  this  is  that  the  sugar  of  the 
apple  juice  is  changed  into  alcohol 
and  carbon  dioxide.  Yeast  cells 
which  are  in  the  air  fall  into 
the  juice  and  cause  this  change 
(cf.  §  201). 

When  the  hard  cider  is  allowed 
to  stand  longer,  a  mold  called 
"mother"  begins  to  grow  in  it; 
this  changes  the  alcohol  to  acetic 
acid  and  we  then  have  cider  vine- 
gar. Grape  juice  is  changed  in 
the  same  way,  first  into  wine, 
which  contains  alcohol  and  carbon  dioxide,  then  into 
wine  vinegar,  which  contains  acetic  acid. 

Milk  sours  because  one  particular  kind  of  ferment  gets  into  milk 
and  changes  the  sugar  of  milk  into  lactic  acid.  This  acid  causes  the 
milk  to  become  curdy  and  to  taste  sour.  The  same  acid  is  present 
in  dill  pickles  and  sauerkraut. 

Many  fruits,  such  as  tomatoes,  cherries,  and  green  apples,  and 
some  plant  stems,  such  as  rhubarb  and  sour  grass,  are  strongly  acid. 
Lemons,  oranges,  and  grapefruit  contain  citric  acid ;  grape  juice  con- 
tains tartaric  acid. 

All  of  the  acids  we  have  named  are  compounds  of  carbon,  hydrogen, 
and  oxygen.  There  is  also  another  very  important  acid  which  con- 


FIG.  102.  —  We  make  vin- 
egar by  letting  the  air  -oxidize 
fermented  fruit  juices,  so  that 
their  alcohol  is  changed  to 
acetic  acid. 


ACIDS  AND  ALKALIES  193 

tains  sulphur,  hydrogen,  and  oxygen ;  this  is  sulphuric  acid,  or  vitriol. 
Hydrochloric  acid  is  another  very  important  acid.  Its  old  name  is 
"  muriatic  "  acid.  It  contains  hydrogen  united  with  chlorine.  Chlo- 
rine, you  remember,  is  present  in  salt. 

176.  What  Makes  a  Compound  an  Acid?  —  In  telling 
what  acids  are  like,  we  can  say,  first,  that  they  are  sour. 
If  acids  are  strong  enough,  they  will  "  eat  "  the  skin  and 
clothing  upon  which  they  fall.  Metals  are  also  "  eaten,"  or 
"  etched/7  by  acids.  We  have  already  learned  that  in 
making  hydrogen  (cf.  §  114)  zinc 
is  used  up,  or  eaten,  by  the  acid, 
and  disappears.  Are  copper  and  r 
lead  used  for  cooking  vessels? 
They  cannot  be,  because  the  acids 


in  foods  act  upon  the  metals  and      FlG    103  _  The  metal  is 

Cause     poisonOUS     Compounds     Of    eaten  out,   or  etched  wherever 
,  .        ,          .  it  is  exposed  to  the  action  of 

copper  and  lead  to  be  formed.        the  acid. 

Have  you  ever  seen  copper  which  has  been  etched  so  that  it  shows 
a  beautiful  design,  as  in  Fig.  103?  The  design  is  made  by  covering 
all  the  copper,  except  where  the  lines  are  to  be,  with  asphalt  paint. 
Then  the  copper  is  put  into  nitric  acid ;  the  acid  eats  it  wherever  it  is 
not  covered.  When  the  copper  is  removed  from  the  acid,  the  asphalt 
is  scraped  off  and  there  is  a  design  on  the  copper. 

Acids  also  act  with  marble,  limestone,  or  soda.  When 
an  acid  is  mixed  with  marble,  carbon  dioxide  is  given  off 
(cf.  §38).  This  causes  a  great  deal  of  bubbling,  or 
effervescence.  Bones,  which  contain  much  limestone, 
lose  their  stiffening  (largely  limestone)  by  being  placed 
in  an  acid.  Why  can  a  dog  eat  bones?  Can  it  be  that 


194  JUNIOR  SCIENCE 

the  acid  in  the  dog's  stomach  is  strong  enough  to  destroy 
the  hard  part  of  the  bone  ? 

177.  What  are  Bases  Like  ?  —  Have  you  ever  tried  to 
wash  a  greasy  pan  with  water  alone?  If  you  have,  you 
know  how  hard  it  is  to  remove  the  grease,  because  it 
doesn't  mix  with  the  water.  But  if  you  put  into  the 
greasy  pan  some  lye,  or  other  washing  powder,  and  add 
warm  water  to  it,  you  find  that  the  grease  is  easily  washed 
off.  It  seems  to  dissolve  and  disappear.  The  lye  and 
washing  powder  belong  to  the  class  of  substances  we  call 
bases.  We  say  they  "  cut  "  grease. 

The  chemist  says  lye  is  sodium  hydroxide,  to  show  it  is 
composed  of  the  elements  sodium,  hydrogen,  and  oxygen. 
Potash  lye  is  called  potassium  hydroxide.  What  elements 
does  it  contain  ?  Do  you  know  what  ammonia  water  is  ? 
It  is  a  very  strong-smelling  liquid  that  acts  in  many  ways 
like  lye.  You  put  some  into  water  that  you  use  for  wash- 
ing windows  or  glassware,  because  it  removes  grease  and 
makes  the  glass  bright  and  clean.  Like  lye  it  is  a  base. 

There  is  another  very  common  base  ;  it  is  lime.  Have 
you  ever  seen  masons  making  mortar?  They  put  lumps 
of  a  white  solid  (lime)  into  the  vats  of  water,  and  the  lime 
unites  so  vigorously  with  the  water  that  the  water  be- 
comes almost  boiling  hot.  The  product  is  slaked  lime. 
Masons  mix  sand  with  the  slaked  lime  and  produce 
mortar.  Lime  will  destroy  animal  substances,  so  men 
are  able  to  use  it  for  taking  hair  off  from  hides.  Its 
solution,  limewater,  can  be  added  to  milk  to  sweeten  it, 
if  it  has  become  slightly  sour.  Limewater  mixed  with 
olive  oil  is  used  to  heal  burns. 


ACIDS  AND  ALKALIES  195 

The  strong  bases  all  have  a  bitter  taste  even  when  dissolved  in  a 
great  deal  of  water.  If  there  is  not  much  water  mixed  with  the  bases, 
their  solutions  will  destroy  skin  and  flesh  and  the  mucous  membrane 
that  lines  the  mouth.  Hence  we  must  use  a  great  deal  of  care  in 
handling  lye. 

178.  How  Can  We  Test  for  Bases  and  Acids?  — How 

do  bases  differ  from  acids  ?  If  you  had  a  solution  which 
looked  like  water,  and  yet  you  knew  that  it  might  con- 
tain an  acid  or  a  base,  how  would  you  find  out  which  it 
was?  The  easiest  way  is  to  use  litmus.  Litmus  is  a 
coloring  matter  obtained  from  lichens,  a  kind  of  plant. 
An  acid  will  turn  blue  litmus  to  red.  A  base  will  turn 
red  litmus  to  blue.  Litmus  may  be  used  in  the  form  of 
a  solution  and  a  few  drops  of  it  may  be  poured  into  the 
liquid  you  are  testing ;  or  it  may  be  in  the  form  of  colored 
paper  and  a  slip  of  the  paper  may  be  dipped  into  the 
liquid.  If  you  test  orange  juice,  what  happens  to  your 
litmus?  Test  some  of  the  things  you  find  at  home  to 
see  which  show  an  acid  test  and  which  show  a  basic  test. 
Also  bury  a  piece  for  an  hour  or  two  in  some  moist  soil 
in  a  flower  pot  and  see  whether  the  soil  is  acid  or  not. 
Farmers  use  this  test,  because  acid  soil  is  not  good  for 
the  raising  of  most  crops.  Purple  cabbage  solution  may 
be  used  in  exactly  the  same  way  as  litmus  solution. 

179.  How  Does  an  Acid  Act  with  a  Base?  —  We  can 
now  learn  something  still  more  interesting  about  acids 
and  bases.     Dip  your  thumb  and  forefinger  into  a  solu- 
tion of  caustic  lye  and  then  rub  them  together.     They 
feel  slippery,  or  slimy,  do  they  not,  as  though  they  were 
covered  with  strong  soap  solution?     Now  add  to  the 


196  JUNIOR  SCIENCE 

lye  solution  some  vinegar,  or  lemon  juice,  a  little  at  a 
time.  You  will  soon  find  that  the  solution  no  longer  has 
the  slimy  feel  it  had  at  first.  The  acid  of  the  vinegar  or 
lemon  juice  has  destroyed  this  power  of  the  lye.  The 
chemist  says  the  acid  has  neutralized  the  lye. 

Put  .a  piece  of  red  litmus  paper  into  some  fresh  caustic 
lye  solution;  what  color  does  the  litmus  have  now? 
Then  add  some  hydrochloric  acid  solution,  little  by 
little,  to  the  lye  solution,  stirring  as  you  do  so.  What 
color  does  the  litmus  take  on?  The  acid  has  neutral- 
ized, or  destroyed,  the  power  of  the  lye  to  turn  litmus 
blue. 

If  there  is  no  base  left  in  the  lye  solution  to  which  the 
hydrochloric  acid  was  added,  what  do  you  suppose  is 
left  ?  Put  the  solution  into  a  saucer  or  into  an  evaporat- 
ing dish,  and  drive  off  the  water  by  heating  the  dish  gently. 
What  is  left  in  the  dish  ?  Taste  it ;  it  is  common  salt. 
So  salt  was  formed  when  caustic  lye  was  neutralized  by  hy- 
drochloric acid.  When  vinegar  or  lemon  juice  neutralizes 
the  caustic  lye  solution,  there  is  another  substance  formed 
which  is  not  common  salt,  but  is  like  it  in  some  ways. 
The  chemist  calls  all  such  substances  salts,  since  they 
are  formed  by  the  neutralization  of  a  base  by  an  acid, 
as  common  salt  is. 

Salts  are  very  common.  Marble,  limestone,  table  salt, 
blue  vitriol,  saltpeter,  and  alum  are  all  called  salts  by 
the  chemist. 

180.  Exercises. —  1.  Galvanized  iron  is  iron  covered  with  zinc. 
Is  it  a  safe  material  for  dishes  in  which  acid  fruits  are  cooked? 

2.   The  acid  present  in  canned  tomatoes  causes  milk  to  become 


ACIDS  AND  ALKALIES  197 

curdy.     In  making  "  cream  tomato  "  soup  some  baking  soda  is  added 
to  the  tomato  to  prevent  the  curding ;  explain  how  it  acts. 

3.  The  spots  of  limestone  on  a  glass  water  pitcher  are  easily  re- 
moved by  a  little  vinegar  or  lemon  juice.     Can  you  tell  why? 

4.  Collect  some  wood  ashes,  cover  them  with  water,  and  after  the 
ashes  have  settled,  pour  off  the  water.    Then  test  the  water  with  pink 
and  blue  litmus  paper.     Does  the  solution  have  an  acid  or  a  basic 
action?     Could  you  use  wood  ashes  to  "  sweeten  "  a  "  sour  "  soil? 

5.  Test  solutions  of  alum,  washing  soda,  and  common  salt  sepa- 
rately with  pieces  of  red  and  blue  litmus.     How  does  each  behave? 

6.  To  a  lump  of  old  mortar  in  a  dish  add  a  few  drops  of  a  dilute 
acid.     Describe  what  happens.     Can  you  prove  that  the  gas  formed 
is  carbon  dioxide?     What  is  left  undissolved?     What  gas  does  fresh 
mortar  take  from  the  air  as  it  hardens,  or  sets? 


CHAPTER   XIX 
WASHING  AND   CLEANING 

181.  What  are  the  Materials  of  Clothing?  —  In  very 
ancient  times  savage  men  kept  warm  by  clothing  them- 
selves with  the  skins  of  animals ;  even  today  furs  are 


(  Copyright  by  Mclntosh  Stereoptlcon  Co.) 
FIG.  104.  —  A  cotton  field  of  the  South. 

sometimes  used  for  warmth  as  well  as  for  decoration. 
Still,  as  you  know,  the  common  materials  for  our  cloth- 

198 


WASHING  AND   CLEANING 


199 


Cotton 


Flax 


ing  are  woven  fabrics ;  they  come  from  both  animal  and 
vegetable  sources.  Silk  and  wool  are  from  animals; 
while  the  vegetable  fibers  which  can  be  woven  to  ad- 
vantage are  cotton  and  flax.  What  an  interesting  story 
it  would  be,  if  we  could  learn  how  men  first  came  to  use 
these  materials  for 
their  clothing. 

Cotton  plants 
have  a  fluffy,  soft 
covering  made  of 


long  fibers  for  their 
seeds  (Fig.  105). 
Men  gather  this 
covering  from  the 
plant,  separate  it 
from  its  seeds,  and 
use  the  fibers  in 
making  cotton 
cloth.  The  fibers 
are  hollow  tubes, 
flat  and  twisted. 

The  stalks  of 
the  flax  plant  are  used  to  make  linen  cloth.  These 
fibers  are  hollow,  like  those  of  cotton,  but  straight  in- 
stead of  being  twisted.  They  have  thick  walls  with 
central  openings.  Linen  cloth  is  stronger  than  cotton, 
but  cotton  is  the  lighter  and  more  elastic. 

Cotton  and  linen  are  easily  destroyed  by  strong  acids,  but  are  not 
easily  harmed  by  bases.  In  fact,  if  cotton  is  soaked  in  a  strong  base 
for  a  short  time,  and  is  then  washed  thoroughly,  it  is  made  stronger 


Silk 
Fibers 


FIG.  105.  —  The  fibers  out  of  which  fabrics  are 
woven,  and  the  silkworm's  cocoon.  Note  the 
overlapping  scales  of  wool  fibers. 


200  JUNIOR  SCIENCE 

and  has  a  glossy,  silky  appearance.    Cotton  thus  treated  is  called 
<4  mercerized  "  cotton. 

182.  How  Are  Silk  and  Wool  Obtained  ?  — Silk  and 
wool  are  obtained  from  animals.  Silk-growing  is  one  of 
the  greatest  industries  of  Japan  and  China.  The  eggs 
of  the  silkworm  are  allowed  to  hatch  in  long  trays.  These 
trays  are  filled  with  leaves  and  the  tiny  "  worms  "  feed 
upon  these  leaves  until  they  become  large,  fat,  white 
creatures.  There  are  usually  so  many  of  these  "  worms  " 
feeding  in  a  room  that  you  can  hear  them  crunch  their 
food. 

When  the  silkworm  is  grown,  it  spins  a  cocoon,  as  our 
common  caterpillars  do,  and  prepares  to  come  out  a 
beautiful,  winged  creature.  But  after  the  spinning  is 
completed,  men  place  the  cocoon  in  hot  water  to  kill 
the  silkworm ;  then  they  unwind  the  tiny  thread  which 
forms  the  cocoon.  Many  of  these  threads  are  woven 
together  to  give  us  a  little  piece  of  silk  cloth.  Silk  fibers 
are  long,  smooth,  beautiful,  and  very  strong. 

Wool  is  obtained  by  shearing  sheep ;  this  is  done  in 
the  spring  time.  The  heavy,  wool  coat  grows  in  the 
autumn  to  protect  the  animal  from  winter's  cold  and 
will  drop  off  when  warm  weather  comes,  if  it  is  not  cut. 
The  fibers  of  wool  are  short  and  thick,  with  projections 
that  overlap  one  another  (Fig.  105). 

Unlike  vegetable  fibers,  animal  fibers  are  destroyed 
by  bases,  and  are  not  readily  acted  upon  by  acids.  No 
method  of  washing  wool  should  be  used  which  will  force 
the  cells  closer  together,  or  the  wool  will  slirink  and 
finally  become  stiff  and  board-like. 


WASHING  AND   CLEANING 


201 


183.  How  Is  Clothing  Washed  ?  —  When  fibers  are 
woveii  into  cloth,  tiny  spaces  (pores)  are  left  between 
the  threads  of  the  cloth.  These  pores  form  an  absorbing 
surface  for  the  skin  (cf.  §  108).  Perspiration  and  the 
waste  it  removes  from  the  body,  as  well  as  dead  skin 


(Courtesy  oftheJudd  Laundry  Machine  Co.) 
FIG.  106.  —  The  equipment  of  a  modern  laundry.    Name  the  different  machines. 

itself,  are  all  caught  in  the  surface  of  the  cloth.  Clothing 
that  has  been  worn  too  long  has  a  damp,  sticky  feel 
because  its  pores  are  filled.  This  clothing  should  not  be 
worn  again  until  it  has  been  washed.  The  reason  why 
clean  garments  "  feel  so  good/7  as  we  say,  is  because 
they  have  a  fresh  absorbing  surface. 


202  JUNIOR  SCIENCE 

In  ancient  times  the  women  took  the  soiled  clothing  of  the  family 
to  a  stream  and  rubbed  it  out  upon  the  rocks.  Later  the  washing 
was  done  at  home  with  the  aid  of  hot  water  and  soap.  Now  we  have 
stationary  tubs,  washing  machines,  wringers,  and  even  machines  run 
by  electricity  (Fig.  106).  So  our  washing  is  done  better  and  done 
more  easily  all  the  time,  as  we  recognize  the  importance  of  clean 
clothing.  What  would  you  think  of  the  practice,  common  in  some 
countries,  of  sewing  on  heavy  clothing  in  the  fall  and  leaving  it 
on  all  winter? 

184.  How  Does  Soap  "  Work  "  ?  —  Why  do  we  use 
soap?  We  say  that  it  removes  dirt.  If  you  think  of  it, 
you  will  see  that  the  dirt  we  want  taken  away  from  cloth- 
ing is  usually  some  form  of  grease  or  some  form  of  soot. 
When,  therefore,  the  soap  solution  is  rubbed  on  greasy 
cloth,  it  breaks  up  the  grease  into  tiny  droplets  and 
surrounds  them.  Thus  they  are  separated  from  the 
cloth  and  can  be  washed  away  by  the  water.  Water 
alone  cannot  do  this. 

If  you  try  the  action  of  soap  upon  some  kerosene,  you 
can  understand  its  cleaning  power  for  grease.  Into  a 
test  tube  or  small-mouth  bottle  put  some  kerosene  and 
water  and  shake  the  two  together.  The  kerosene  will 
break  up  into  droplets,  but  when  you  stop  shaking,  the 
droplets  will  soon  unite  and  the  layer  of  kerosene  will 
float  upon  the  layer  of  water.  But  if  you  shake  the 
kerosene  with  a  dilute  soap  solution,  the  kerosene  does 
not  separate  again  into  a  layer  by  itself;  it  remains  as 
tiny  droplets  mixed  with  the  soap  solution.  In  the  same 
way,  the  butter  fat  of  milk  is  kept  suspended  in  tiny 
droplets  by  something  in  the  milk.  A  mixture  like  this 
is  called  an  emulsion. 


WASHING  AND   CLEANING 


203 


When  a  soap  solution  is  rubbed  upon  soot,  the  tiny 
particles  of  soot  are  surrounded  by  the  soap  solution  and 
so  taken  off  the  clothing. 

How  do  you  suppose  people  ever  learned  to  use  soap  ? 

185.  How  Is  Soap  Made  ?  —  In  primitive  times  soap- 
making  was  carried  on  by  every  family  (Fig.  107).  In 
the  spring  all  the  winter's  wood  ashes  were  pounded  down 
in  a  barrel  and  water  was  ^^ 
allowed  to  soak  through 
the  ashes  and  caught 
when  it  came  out  at  the 
bottom.  This  water  was 
boiled  down  to  form 
homemade  lye  (potash). 
Later,  lye  was  bought 
instead  of  being  made. 
Then  the  lye,  either  home- 
made or  commercial,  was 
placed  in  a  huge  kettle 
with  melted  fat  (from 
the  winter's  supply  of 
meat)  and  the  two  were  cooked  together  in  the  open. 
Sometimes  the  cooking  was  continued  for  two  or  three 
days.  Then  the  "  soft  soap  "  was  cooled  and  put  away 
in  barrels  for  the  next  year's 


FIG.  107.  —  The  making  of  soap  at  home 
by  the  cooking  of  grease  and  lye. 


Nowadays  soap  is  made  on  a  large  scale  in  factories  (Fig.  108). 
Nearly  every  meat-packing  house  has  a  soap  factory  as  a  part  of  its 
business.  Why?  When  the  meats  are  cut  and  packed,  there  are 
always  fat  portions  that  cannot  be  sold.  These  are  used  to  make 
soap.  Some  soaps  are  made  of  vegetable  fats,  such  as  olive  oil  and 


204  JUNIOR  SCIENCE 

cottonseed  oil,  instead  of  animal  fats.  Soap  is  made  by  boiling  the 
fat  or  oil  with  sodium  hydroxide  (lye).  The  lye  "  cuts  "  the  fat  and 
it  disappears  into  solution.  Common  table  salt  is  then  added  to  the 
solution,  and  the  soap  is  "  salted  out."  It  floats  on  the  top,  is  skimmed 
off,  pressed,  and  cut  into  cakes.  Sometimes  a  longer  process  is  used, 
so  that  glycerine  can  be  made  at  the  same  time.  What  sort  of  sub- 
stance is  glycerine?  What  are  some  of  its  uses? 


(Courtesy  of  Swift  &  Co.) 

FIG.  108.  —  How  soap  is  made  on  a  large  scale.     Such  kettles  are  three  stories 
high  and  hold  enough  material  to  make  about  700,000  bars  of  soap. 

186.  What  is  Dry  Cleaning  ?  — Certain  materials, 
such  as  silks,  woolens,  and  kid  gloves,  lose  their  soft 
finish  if  they  are  washed  often,  as  cotton  and  linen  goods 
are.  For  this  reason  a  dry  cleaning  shop  is  now  found 
in  even  our  small  cities.  Dry  cleaning  is  done  by  means 
of  gasoline  instead  of  water.  The  gasoline  used  for  the 
cleaning  evaporates  quickly  from  the  material,  leaving 
it  clean  and  soft  and  as  pretty  as  when  new.  People 


WASHING  AND   CLEANING  205 

think  of  gasoline  as  a  liquid ;  they  should  think  of  it  as 
an  inflammable  gas.  It  must  not,  therefore,  be  used 
near  a  fire  nor  where  its  vapor  can  be  carried  to  the  fire, 
or  it  may  burn  with  a  frightful  explosion. 

187.  Exercises. —  1.   Why  cannot  clothing  be  washed    properly 
in  water  alone,  without  soap  ? 

2.  Laundries  sometimes  use  acids  for  the  washing  of  clothing ;  do 
you  think  such  fabrics  will  last  long?     What  ones  are    especially 
injured? 

3.  Ask  a  good  laundress  how  woolen  clothing  should  be  washed  so 
that  it  will  remain  soft  and  porous. 

4.  Find  out  why  "  bluing  "  is  used  in  the  washing  of  white  goods. 

5.  Does  soap  form  suds  as  quickly  in  well  water  as  in  rain  water? 
Why? 

6.  Soak  some  "  strong  "  laundry  soap  in  a  little  water  and  test 
the  solution  with  litmus  papers.     Is  the  solution  acid  or  basic?     Do 
the  same  with  some  washing  powder.    Why  is  strong  laundry  soap 
not  good  for  your  hands? 

7.  Why  is  starch  used  in  the  laundry? 

8.  Is  it  true  that  the  civilization  of  a  country  can  be  told  from 
the  amount  of  soap  it  uses?     Why? 

9.  Can  you  give  a  good  reason  why  towels  should  not  be  ironed? 


CHAPTER  XX 
FOOD 

188.  Why  Do  We  Need  Food?  —  If  we  want  to  take 
a  trip  in  an  automobile,  we  are  very  careful  to  fill  the 
gasoline  tank  before  we  start.  When  we  are  traveling 
across  the  country  on  a  train,  the  train  stops  at  certain 
places  and  takes  on  coal  or  water.  If  cars  and  trains 
run,  they  must  be  fed  with  gasoline  or  coal  or  other  fuels. 
It  is  the  same  with  our  bodies.  If  we  want  to  walk  and 
move  about,  our  bodies  must  have  something  to  burn, 
in  order  that  they  may  have  energy.  Now  the  body 
does  not  burn  gasoline  as  a  car  does,  or  coal  as  an  engine 
does ;  it  burns  food.  The  food  which  we  eat  is  oxidized 
in  the  same  way  as  the  gasoline  and  coal  are  (cf .  §  32) 
and  yields,  as  they  do,  heat  and  energy. 

However,  there  is  one  important  difference  between 
the  human  engine  and  the  steam  engine :  the  human 
machine  is  not  built  in  its  final  form ;  it  has  to  grow.  It 
wears  out,  too,  and  has  to  make  its  own  repairs. 

Therefore  two  kinds  of  food  are  needed  for  the  human 
engine :  foods  that  will  be  burned,  or  oxidized,  so  that 
we  may  have  energy,  and  foods  of  the  other  sorts  to  be 
used  for  the  growth  and  repair  of  the  body. 

Think  of  all  the  different  kinds  of  food  we  eat,  yet  all 
these  may  be  divided  into  five  classes  of  foods.  They 
are: 

206 


FOOD 


207 


1.  Carbohydrates. 

2.  Fats. 

3.  Nitrogenous  foods. 


4.  Minerals. 

5.  Water. 


The  first  two  are  of  use  in  furnishing  energy,  while 
the  third  is  needed  for  building  up  new  tissues  and  re- 
pairing old  ones.  See  Fig.  109. 

189.  What  Foods  Give  Us  Energy?  —  Carbohydrate  is 
a  long  word,  but  it  means  foods  like  sugar,  starch,  and 
cellulose.  Carbohydrates  and  fats  are  all  compounds 


Fats 


Water 


Carbohydrates    Water 


Fats 


Proteids 


Minerals 

and  Fats 

Carbohydrates 


Minerals 
Proteids  and  Fats 


Minerals 


FIG.  109.  —  The  amounts  of  the  different  classes  of  foods  present  in  an  egg, 
a  potato,  a  loaf  of  bread,  and  a  sirloin  steak. 

of  carbon,  hydrogen,  and  oxygen.  When  they  are  taken 
into  the  body,  they  combine  with  more  oxygen  (obtained 
through  the  lungs)  until  the  carbon  and  hydrogen  are 
both  completely  oxidized.  This  process  of  oxidation  is 
accompanied  by  heat.  The  heat  keeps  the  body  warm 
and  makes  movement  possible.  Why  are  girls  and  boys 
hungry  after  playing  tennis,  or  hockey,  or  football? 
Why  are  they  warm  ? 

The  carbohydrates  are  found  almost  entirely  in  vege- 
table foods.  Except  in  milk,  only  traces  of  them  are 
found  in  any  animal  food. 


208  JUNIOR  SCIENCE 

The  fats,  the  other  great  class  of  energy  producers,  are 
found  in  both  vegetable  and  animal  foods.  They  are 
the  oils  and  solid  fats,  such  as  beef  suet,  tallow,  lard, 
olive  oil,  cottonseed  oil,  and  butter  (Fig.  110).  The  fats 


(Copyright  by  Mclntosh  Slereopticon  Co.) 
FIG.  110.  —  Removing  the  butter  from  the  churn  in  a  large  creamery. 

have  a  greater  proportion  of  carbon  than  the  carbohy- 
drates, and  therefore  produce  more  heat  when  oxidized. 
A  pound  of  fat  produces  2 J  times  as  much  heat  as  a  pound 
of  sugar  or  starch. 

190.  What  Foods  Make  Us  Grow?  —  Every  living 
organism  or  cell  contains  nitrogen,  therefore  foods  which 
contain  nitrogen  are  needed  to  build  new  cells  or  repair 


FOOD  209 

the  old  ones.  Such  foods  are  known  as  nitrogenous 
foods.  They  contain  hydrogen,  oxygen,  carbon,  and 
nitrogen.  True,  if  an  excess  is  eaten,  the  hydrogen  and 
carbon  may  be  oxidized  to  furnish  energy  just  as  the 
sugars  and  fats  do.  In  that  case,  the  nitrogen  is  wasted 
and  forms  compounds  which  are  difficult  for  the  body 
to  get  rid  of.  For  that  reason,  and  because  the  nitrogen 
foods  are  usually  more  expensive,  it  is  wise  to  eat  only 
as  much  of  them  as  the  body  actually  needs  for  growth 
and  repair,  and  to  depend  solely  upon  the  other  foods 
(carbohydrates  and  fats)  for  heat  and  energy.  Nitrogen 
cannot  be  stored  in  the  body  as  sugars  and  fats  can.  If 
carbon,  oxygen,  and  hydrogen  are  stored,  they  are 
changed  to  a  form  of  fat  and  do  not  hold  the  nitrogen. 
How  often  should  we  eat  meat  (a  nitrogenous  food) 
during  the  day  ? 

Lean  meat,  of  course,  is  the  most  common  food  of  this 
class.  Milk,  cheese  (a  product  of  milk),  eggs,  meat,  nuts, 
peas,  beans,  and  lentils  are  the  foods  which  contain  the 
most  nitrogen,  and  are  called  the  tissue-builders,  or  the 
nitrogenous  foods.  They  are  also  sometimes  called  pro- 
teid  foods. 

An  Experiment.  —  Do  you  want  to  separate  the  starch  from  the 
nitrogenous  part  of  wheat  flour?  Then  make  a  tough  dough  out  of 
}  of  a  cupful  of  flour  and  a  little  water.  Tie  the  dough  hi  a  piece  of 
good  cheesecloth  and  knead  the  dough  under  water.  Note  that  the 
water  becomes  cloudy  because  of  the  starch  that  comes  through  the 
cloth.  After  no  more  starch  can  be  pressed  out  of  the  flour,  examine 
the  substance  inside  the  cloth.  What  is  its  color?  Is  it  sticky? 
Elastic?  It  is  the  gluten,  the  nitrogenous  part  of  the  flour.  Let  the 
starchy  water  settle,  then  pour  off  all  the  water  you  can  and  the  starch 


210 


JUNIOR  SCIENCE 


FIG.   111.  —  The  cheesecloth 


will  remain  as  a  sediment.  Scrape  the  starch  out  on  a  piece  of  news- 
paper, and  let  it  dry. 

191.  What  are  the  Minerals  in  Foods  ?  —  The  minerals 
found  in  some  foods  and  water  are  often  called  the  body 
regulators.  Our  table  salt  is  a  mineral  without  which 
we  cannot  exist.  One  of  the  most  cruel  methods  the 
ancients  had  of  inflicting  punishment  upon  prisoners 

was  to  kill  them  by  leaving  salt 
out  of  their  food.  They  died  a 
slow,  painful  death. 

Some  foods,  such  as  spinach, 
lettuce,     onions,     and    different 
bag  contains  wheat-flour  dough,   greens,  consist  almost  entirely  of 

When  this  is  kneaded  under  Wofpr  r^nrj  rrnnprnlQ  ~PYnit«  anrl 
water,  the  starch  of  the  flour  waler  an(  rals- 

passes  through  the  cloth,  leav-  vegetables  are  rich  in  mineral  mat- 
ing the  gluten  inside.  ,—,,  ,  ,  .  , 

ter.     ihe    elements    which    are 

required  by  the  body  are  sulphur  (found  in  great  amounts 
in  eggs),  calcium  (best  source  is  in  milk),  potassium, 
phosphorus,  chlorine,  iron,  and  others.  Our  bones  are 
made  largely  of  calcium  compounds.  If  we  do  not  have 
enough  of  these  compounds,  we  are  likely  to  be  weak- 
boned  or  undersized.  At  what  ages  do  we  need  the 
most  calcium  ?  Experts  say  that  young  children  should 
have  a  quart  of  milk  a  day  and  that  older  boys  and 
girls  should  have  at  least  a  pint  in  order  to  be  sure  to  get 
enough  calcium  compounds. 

When  iron  is  lacking  in  the  diet,  the  disease  anemia 
lays  hold  upon  the  person.  Many  pale  children  who 
seem  dull  and  lifeless  are  suffering  because  there  is  not 
enough  iron  in  the  blood.  The  body  cannot  digest  nails 


FOOD  211 

or  a  bar  of  iron,  so  we  must  get  our  iron  by  eating  those 
foods  which  are  rich  in  it.  Spinach  is  especially  rich  in 
iron ;  so  are  eggs.  Raisins,  dates,  figs,  and  prunes  give 
it  in  quantities  we  can  measure,  and  many  vegetables 
contain  a  small  per  cent  of  iron. 

Many  people  believe  that  a  diet  of  meat,  potatoes,  and  bread  is 
sufficient  to  keep  them  in  health.  This  is  a  mistake.  If  we  wish  to 
have  splendid  health  and  the  perfect  kind  of  body  which  has  no 
weak  points  and  so  can  resist  disease,  we  must  be  careful  to  add  milk 
to  the  list  and  to  eat  plenty  of  fresh  fruits  and  vegetables.  Only  thus 
can  we  get  the  precious  minerals  we  need. 

When  any  food  is  burned  completely,  the  ashes  which  remain  are 
the  minerals  contained  in  that  food. 

Experiment.  —  Set  the  cover  of  a  baking-powder  can  upon  some 
hot  coals,  or  over  a  gas  flame,  and  in  it  heat  a  small  piece  of  bread  until 
all  the  charcoal  has  burned  away  and  only  grayish  ashes  remain.  Is 
the  amount  great  or  small?  Put  the  ashes  in  a  glass  dish  and  add  a 
drop  of  some  acid.  What  happens?  What  gas  is  probably  given  off 
(cf.  §38)? 

192.  Why  Do  We  Need  Water  in  the  Diet?  —  Every 
food  contains  some  water,  and  some  foods,  such  as  milk, 
are  mostly  water.  Water  is  the  most  important  thing 
in  the  diet.  Man  can  live  without  food  for  days  and  days, 
but  water  is  absolutely  necessary  if  life  is  preserved  for 
long.  Water  is  used  in  building  up  the  tissues,  in  carry- 
ing them  supplies,  and  in  carrying  away  wastes.  Drink- 
ing water  at  meal  time  is  not  harmful,  if  we  do  not  "  wash 
down  "  half-chewed  portions  of  food  with  it.  A  drink  of 
water  a  little  while  before  eating  is  of  great  benefit  in 
preparing  the  digestive  organs  for  receiving  food.  Some 
physicians  advise  the  drinking  of  eight  glasses  of  water 


212 


JUNIOR  SCIENCE 


STARCH 


OTL 


every  day ;  others  say  more  or  less.  It  is  well  for  us  to 
cultivate  the  habit  of  drinking  a  great  deal  of  water ;  we 
shall  have  better  health  if  we  do. 

193.   How  Do  We  Depend  upon  Plants  ?  —  Could  we 
live  without  plants?     No,  we  could  not.     Can  we  take 
a  pinch  of  sulphur,  a  bit  of   carbon   from  coal,  and   a 
quart  of  nitrogen  from  the  air?     The  question  is  ridicu- 
lous ;  yet  we  have  to 
have    those   very   ele- 
ments if  we  would  live. 
That    is    what    plants 
do   for  us.     Minerals, 
EMBRYO   water,  and  the  nitrogen 
PLANT     and  the  carbon  dioxide 
of  the  air  are  all  taken 
into  the  plant  as  foods 
FIG.  112.  —  A  kernel  of  corn,  showing  how   and  are  made  part  of 

the  corn  grain  is  stored  with  food  (largely  f^  nlont'Q  hnrlv  TViP 
starch)  for  the  young  corn  plant.  ^^ 

plant  unites  them  into 

complex  compounds,  such  as  sugars,  oils,  and  nitrogenous 
substances.  Then  animals  eat  the  plants  and  get  the 
food  materials  from  them  in  a  useful  form.  The  animal 
food  which  we  eat,  such  as  meat,  eggs,  and  milk,  was 
formed  by  an  animal  from  plant  food  eaten  by  that 
animal  or  by  smaller  animals  upon  which  it  feeds.  What 
do  sheep  feed  upon  ?  Chickens  ? 

To  make  a  carbohydrate,  carbon  dioxide  is  taken  from  the  air  and 
by  a  process  which  goes  on  in  the  plant  is  joined  with  water  to  form 
sugar  or  starch.  These  are  oxidized  in  the  animal  body  to  give  water 
and  carbon  dioxide  again.  Thus  plant  life  and  animal  life  help  each 
other  and  a  delicate  balance  is  kept  between  the  two. 


FOOD 


213 


The  plant  stores  food  to  nourish  its  young.  Examine 
a  kernel  of  corn  (Fig.  112).  You  will  find  there  is  a 
small  dark  spot  at  the  tip.  This  is  the  germ,  or  living 
part,  which  will  start  growing  if  put  into  water.  The 
greater  part  of  the  kernel  is  a  white  substance,  starch 
(Fig.  113).  This  starch  is  stored  around  the  germ  so 
that  the  little  plant  when  it  starts  growing  will  have 
some  food  close  at  hand  in  a  form 
easy  to  use. 

It  is  these  plant  storehouses 
that  we  usually  eat.  Sometimes 
we  eat  the  leaves  (spinach),  some- 
times the  stalk  (celery),  but  more 
often  it  is  the  seed  (peas,  beans, 
rice,  wheat)  or  the  fruit  (grapes 
and  oranges).  Roots  and  under- 
ground stems  are  often  the  storing 
places  (potatoes,  radishes,  onions), 
plant  seeds  that  we  use  as  a  food. 

194.   Exercises.  —  1.   Name  the  five  classes  of  nutrients. 

2.  What  are  the  chief  nutrients  in  milk,  meat,  potatoes,  bread, 
sugar,  olive  oil? 

3.  What  is  the  value  of  a  vegetable  salad  in  a  dinner? 

4.  What  nutrients  are  not  abundant  enough  in  a  meal  of  bread, 
boiled  potatoes,  and  rice  pudding? 

5.  What  do  you  think  of  this  as  a  "  balanced  "  or  proper  kind  of 
meal :  meat,  baked  potatoes,  celery  and  baked  apples? 

6.  Why  can  a  dog  digest  bone,  while  we  cannot? 

7.  The  body  temperature  of  some  Arctic  explorers  was  found  to  be 
about  97°  F.  instead  of  98.6°;  why?     What  kinds  of  food  did  they 
need  most? 

8.  Show  that  the  energy  of  your  body  comes  originally  from  the  sun. 


FIG.  113. — Grains  of  starch, 
much  magnified. 

Name  some  other 


CHAPTER  XXI 


THE  COOKING  AND  BAKING  OF  FOODS 

195.  Why  Do  We  Cook  Food?  —  When  in  his  history 
do  you  suppose  man  invented  cooking  ?  No  wild  animal 
cooks  its  food ;  very  early  savage  man  doubtless  ate 

flesh  and  other  foods  raw, 
as  some  savage  races  still 
do. 

No  doubt  the  reason 
why  man  began  to  cook 
food  was  because  he 
found  that  cooking  im- 
proved the  flavor ;  but 
he  has  found,  as  his 
knowledge  has  grown, 
that  the  most  important 
reason  for  the  cooking 
of  food  is  to  make  it 
digest  better.  Cooking  softens  and  breaks  up  the 
walk  which  surround  the  real  food.  These  walls  are  of 
cellulose  in  vegetables  and  of  a  tough  material  called 
connective  tissue  in  meat.  If  you  examine  a  slice  of 
potato  under  the  microscope  (Fig.  114),  you  will  find  that 
it  is  composed  of  many  irregular  cells ;  the  cell  walls  are 
of  cellulose,  the  grains  within  are  grains  of  starch.  Starch 

214 


FIG.  114.  —  A  cross  section  of  potato 
cells,  showing  the  cellulose  walls  and  the 
starch  grains  inside. 


THE  COOKING  AND  BAKING  OF  FOODS 


215 


is  digestible,  but  cellulose  is  not  digested  by  man's  di- 
gestive organs  and  must  be  softened  and  broken  away 
from  the  food  it  wraps,  so  that  the  food  may  be  digested. 
We  find  cellulose  in  fruits  and  vegetables.  The  celery 
plant  has  a  good  deal  of  cellulose ;  the  tough  strings  we 
find  on  old  string  beans  are  cellulose.  The  "  popping  " 
of  corn  illustrates  the  complete  breaking  up  of  the  cellu- 
lose which  in- 
closes the  starch. 

If  you  tear  a 
piece  of  meat  into 
small  pieces  (Fig. 
11 5),  you  will  find 
that  it  is  in  bun- 
dles of  muscle 
fiber  and  that 
each  bundle  is 
made  up  of  sev- 
eral smaller  ones.  Each  big  and  each  little  bundle  is 
surrounded  by  a  coating  of  connective  tissue.  Con- 
nective tissue,  like  cellulose,  needs  to  be  softened  by 
proper  cooking. 

Some  complete  changes  of  one  food  into  another 
occur  in  the  cooking  of  foods,  and  the  new  substances 
are  more  easily  digested.  For  example,  the  brown 
covering  on  toast  is  starch  which  has  been  changed  to 
dextrin,  a  compound  still  more  easily  digested  than 
starch.  When  fatty  meats,  as  bacon,  are  cooked,  some 
of  the  oil  is  lost  by  simply  being  cooked  out,  or  "  tried  " 
out.  Meats,  eggs,  cheese,  and  nitrogenous  foods  of  that 


FIG.  115.  —  A  steak  is  a  cross  section  of  muscle 
tissue.  Note  ,  the  connective  tissue  between  the 
bundles  of  muscle  fiber. 


216  JUNIOR  SCIENCE 

sort  break  up  into  gases  when  heated  to  too  high  a 
temperature,  and  part  of  the  food  is  lost.  What  re- 
mains is  toughened  and  rendered  less  digestible.  Should 
such  foods  be  cooked  at  a  really  high  temperature  ? 

There  is  still  another  reason  for  cooking  food.  When  one  form  of 
animal  or  vegetable  life  lives  upon  another,  that  dependent  form  is 
called  a  parasite.  You  know  that  meat  often  contains  not  only  un- 
desirable bacteria,  but  also  injurious  parasites,  such  as  the  tapeworm 
and  trichina.  For  that  reason  pork,  which  is  more  likely  to  contain 
bacteria  and  parasites  than  any  other  meat,  should  never  be  eaten 
unless  it  has  been  thoroughly  cooked. 

196.  Why  Are  Foods  Cooked  in  Boiling  Water  ?  - 
Foods  which  are  cooked  in  boiling  water  are  cooked  at 
what  temperature?  Of  course  they  are  cooked  at  the 
temperature  of  the  boiling  water,  which  is  212°  F.,  or 
100°  C.  The  cooking  of  vegetables  in  boiling  water  is 
the  simplest  way  of  preparing  them.  Boiling  does  not 
permit  of  any  drying  out  and  most  vegetables  need  water 
to  give  them  a  good  appearance  as  well  as  a  fresh  taste. 
The  objection  to  cooking  in  water  is  that  minerals  and 
other  soluble  materials,  such  as  sugar  and  the  delicate 
oils  which  give  a  food  flavor,  are  lost  in  the  water  and 
drained  off.  We  must  always  take  care  not  to  boil 
food  too  long,  for  over-boiled  vegetables  are  soggy  and 
tasteless. 

The  steaming  of  food  is  an  excellent  method  of  cooking,  with  all 
the  advantages  of  boiling  and  many  more.  Steaming  retains  the 
minerals,  sugar,  and  flavors  in  the  food.  Try  boiling  half  of  a  small 
sweet  potato  and  steaming  the  other  half,  and  compare  the  flavor. 
When  we  cook  food  in  a  steamer,  what  is  it  that  does  the  cooking? 


THE   COOKJNG  AND  BAKINd  OF  FOODS 


217 


197.  What  is  Broiling  ?  —  Broiling  was  the  first  method 
of    cooking    meats.     The    most    primitive    people    built 
fires  and  hung  their  food  over  the  fire  to  brown  (Fig.  116). 
Broiling  is  a  delicious  way  of  cooking  meat,  but  a  pan 
should  be  used  to  catch  the  juices  and  prevent  waste. 

198.  How  Do  We  Fry  Foods  ?  -  -  There  are  two  methods 
of  frying:  deep-fat  frying  and  sauteing.     Sauteing  is  the 
method  used  in  our  ordinary  "  fried  "  potatoes.     Deep- 
fat  frying  is  used  in  cooking 

doughnuts  or  croquettes. 
The  whole  food  is  immersed 
in  the  fat.  Frying  adds  oil 
to  the  food  and  also  adds  to 
the  flavor;  but  it  produces 
a  very  rich  food,  and  the 
stomach  and  other  organs 
cannot  digest  very  much  of  it. 
Fried  potatoes  are  not  health- 
ful when  they  are  "  swimming  in  grease. "  Doughnuts  and 
croquettes  should  be  well  drained  and  the  fat  properly 
hot  to  prevent  them  from  being  soggy  and  greasy.  Fry- 
ing is  the  least  desirable  method  of  cooking,  because  it 
is  likely  to  make  foods  hard  to  digest.  Can  you  name 
four  ways  of  cooking  eggs  besides  frying  them  ? 

199.  What  is  the  Baking  of  Foods  ?  —  Baking  is  not 
limited  to  pies,  cakes,  and  bread ;  vegetables  and  meats 
may  be  baked  also.     Baking  is  the  heating  of  food  in  an 
inclosed  space,  such  as  an  oven.     The  temperature  may 
be  higher  than  boiling  water,  or  it  may  be  lower.     How 
is  the  oven's  temperature  regulated? 


FIG.   116.  —  Broiling  a  fowl  on  a  spit 
over  the  open  fire. 


Corn  starch 


218  JUNIOR  SCIENCE 

Have  you  ever  thought  why  we  should  eat  baked  potatoes  instead 
cf  fried  ones?  Why  are  baked  potatoes  given  to  invalids?  There 
is  a  very  good  reason  for  this.  The  heat  of  the  oven  produces  steam 
inside  -of  the  potato.  The  skin  holds  this  steam  in  and  makes  a 
pressure.  Under  the  pressure  the  starch  cells  burst  and  break  up 
better  than  they  do  if  cooked  in  any  other  way. 

200.   Why  Is  Baking  Powder  Used  ?  —  How  do  you 
think  a  cake  would  look  or  taste,  if  it  did  not  have  any- 
thing in  it  to  make  it  rise  ?     It  would  be  a 
soggy,  lumpy  mass  of  dough  and  very  indi- 
gestible as  well.     How  do  you  suppose  men 

Cream  of  tartar  £  *  f<          •    •  ,J 

first  began  to  use  leavening,  or      raising, 
materials?     There   are   now  two   principal 
ways  of  making  dough  rise.     One  is  by  the 
use  of  baking  powder ;   the  other  is  by  the 
FIG.   117.-     use  of  yeast. 

is  usually  ^  bak-        Cream  of  tartar,  sodium  bicarbonate,  and 
mg     soda,     \    starch  are  used  to  make  the  most  expen- 

cream  of  tartar,        t  ^ 

and    J     com    sive   baking   powders    (Fig.     117) ;    in   the 
cheap  grades,  phosphates  and  alum  are  found. 
Starch  or  flour  is  put  into  the  mixture  to  keep  it  dry. 

When  the  mixture  becomes  moist,  as  when  it  is  mixed 
in  a  batter,  and  particularly  when  it  is  heated,  carbon 
dioxide  is  formed.  The  carbon  dioxide  is  a  gas,  as  you 
know  (cf.  §  37).  When  it  is  formed  in  the  biscuit  or 
cake  dough,  it  pushes  holes  for  itself  in  the  dough.  When 
the  dough  is  placed  in  the  oven,  each  of  these  little,  im- 
prisoned bubbles  of  gas  is  expanded  by  the  heat  and 
pushes  a  larger  hole  for  itself  in  the  dough ;  then  the 
dough  bakes  in  this  raised-up  position. 


THE   COOKING  AND   BAKING  OF   FOODS  219 

What  makes  a  cake  "  fall  "?  The  reason  is  that  if  the  dough  is 
not  thoroughly  cooked  and  stiffened  around  the  bubble,  the  carbon 
dioxide  gas  will  not  remain  expanded  when  the  cake  leaves  the  oven 
and  the  dough  will  sink.  Baking  powder  acts  immediately  upon  being 
moistened  and  anything  which  is  raised  by  baking  powder  should  be 
put  into  the  oven  as  soon  as  it  is  mixed.  What  would  happen  if  it 
were  not? 

201.  What  is  Yeast?  —  For  centuries  people  have 
noticed  that  if  fruit  juices  are  left  in  an  open  dish,  they 
ferment.  Housewives  also  had  a 
way  of  leaving  bread  dough  in  the 
air  and  letting  it  rise,  but  they  did 
not  understand  the  process.  Now 
we  know  that  the  wild  yeast  of  the 
air  caused  it.  Yeast  plants  are  too 
small  for  us  to  distinguish  them  with 
our  unaided  eyes  (Fig.  118). 

The  yeast  has  three  states  of  life:  FIG.  us.  —  Ceiisof  the 
(1)  the  resting  stage;  (2)  the  growing  yeast^ant,  most  of  them 
stage;  (3)  the  spore  stage.  In  the 
resting  stage  yeast  is  blown  against  foods  and  starts  its 
growth.  It  grows  by  "  budding.7'  Each  plant  shoots 
out  several  buds,  which  grow  and  have  buds  of  their 
own  (Fig.  118).  When  the  conditions  for  its  life  are 
very  unfavorable,  each  plant  divides  and  bursts  its  cell 
walls,  throwing  off  spores,  or  "  seed-like  "  forms  of  the 
plant.  These  spores  will  resist  great  changes  of  tem- 
perature for  a  long  time,  are  hard  to  kill,  and  are  con- 
sequently found  everywhere. 

Yeast  requires  certain  sugar  solutions  to  grow  in.  If 
the  solution  does  not  have  too  much  sugar  in  it,  it  will 


220  JUNIOR  SCIENCE 

be  acted  upon  by  yeast  if  left  in  the  air.  The  yeast 
grows  and  changes  the  sugar  into  alcohol  and  carbon 
dioxide  (cf.  §§  175  and  204).  This  is  the  reason  why 
grape  juice,  if  left  in  the  air,  ferments  and  becomes  wine. 

Do  this  experiment  (Fig.  119) :  Place  a  teaspoon  of  molasses  and 
a  cup  of  water  in  a  flask  or  bottle.  Add  J  of  a  cake  of  yeast.  Pro- 
vide a  stopper  with  one  hole  in  it.  Through  this  hole  run  a  glass  tube 
and  let  the  other  end  of  the  tube  dip  under 
the  surface  of  limewater  which  is  in  a  test 
tube  or  slender  bottle.  As  you  found  out  in 
§  37,  carbon  dioxide  makes  limewater  look 
milky.  Leave  the  fermenting  solution  in  a 
warm  (not  hot)  place  for  several  days.  Look 
often  for  any  change  in  the  limewater.  Note 
the  smell  of  the  sugar  solution.  What  has 
FIG.  119.  —  A  sugar  been  formed  in  it?  For  what  is  the  lime- 
solution  (molasses)  being  water  a  test? 
fermented  by  the  action 

of  yeast.     The  test  tube          909      TT  T)npQ     VpflQt       Art      in 

contains  limewater. 

Making  Bread  ?  -  -  The  yeast  we 
buy  and  use  is  grown  in  a  yeast  factory.  The  yeast 
plants  are  produced  in  great  numbers  in  a  food  they 
thrive  on,  then  are  gathered  together  into  yeast  cakes 
and  pressed.  Dry  yeast,  which  contains  the  plants 
in  the  spore  stage,  may  be  kept  for  weeks  or  even  months, 
but  it  takes  longer  to  begin  its  growth  when  it  is  put 
into  the  sponge.  "  Compressed  "  yeast  cakes  are  bought 
in  a  soft  form,  which  contains  the  plants  in  the  growing 
stage,  but  this  form  cannot  be  kept  very  long,  especially 
*n  warm  weather.  The  soft  yeast  has  the  advantage  of 
acting  much  sooner  than  the  dried.  Rising  bread  should 
be  kept  at  about  70°-90°  F.,  as  the  plants  do  not  grow  if 


THE   COOKING  AND  BAKING  OF   FOODS  221 

they  are  too  cool  and  are  easily  killed  (when  growing)  if 
too  hot.  The  yeast  in  the  bread  produces  alcohol  and 
carbon  dioxide,  and  the  carbon  dioxide  and  the  alcohol 
vapor  act  just  as  the  carbon  dioxide  does  when  formed 
from  baking  powder.  The  bubbles  push  the  dough  up 
and  expand  in  the  baking.  During  baking  the  yeast 
plants  are  killed  and  the  alcohol  is  driven  off. 

What  a  wonderful  process  "  raising  bread  by  yeast  "  is ! 

203.   Exercises.  —  1.   What  are  three  good  reasons  for  the  cooking 
of  food? 

2.  Ask  your  mother  or  a  cook  whether  meat  to  be  roasted  should 
be  put  into  a  very  hot  oven  or  one  of  moderate  temperature  and  why. 

3.  Why  is  some  bread  heavy,  or  soggy?     Why  is  it  not  good  to 
eat?     How  is  "  angel  food  "  cake  raised? 

4.  Tell  why  "  toasted  "  bread  is  so  healthful.     Is  a  soft-boiled  egg 
more  digestible  than  a  hard-boiled  one?     Why? 

5.  What  is  the  difference  between  baking  soda  and  baking  powder? 

6.  Soda  and  sour  milk  are  often  used  together  to  make  dough  rise. 
Why?     What  kind  of  substance  does  sour  milk  contain?     How  does 
this  act  with  soda? 

7.  What  nutrients  are  lost  when  food  is  cooked  for  a  long  time 
in  water? 

8.  Find  out  what  foods  can  be  made  out  of  skim  milk. 


CHAPTER  XXII 


THE  PRESERVING   OF  FOODS 

204.   Why  Do  We  Can  and  Preserve  Foods?  —  You 

know  what  happens  if  most  foods  are  left  exposed  to 
the  air  :  they  spoil,  or  "  rot."  The  air  about  us  is  full 
of  the  spores  of  bacteria,  yeast,  and  molds  (cf.  §§  34,  175, 
201),  microscopic  plants  which  include  some  of  man's 

best  friends  as  well  as  some 
of   his   worst   enemies.      As 
they  float  about  in  the  air, 
T^j      the  plant  spores  fall  upon  our 
ill  ft  \  /      foods,  which  are  their  foods 

•^      also  (Fig.  120).     When  these 
tiny  plants   feed    upon   our 

FIG.   120.  —  The  mold  that  grows  J     ^ 

upon  bread,  and  a  fruiting  body  that     f  Ood    they    break    it     Up     into 


the  spores. 


Qf 


which  go  off  as  gases.  In  time  the  food  is  completely 
destroyed.  The  result  of  the  action  of  these  unseen 
destroyers,  when  we  look  at  it  in  the  right  way,  is  really 
very  beneficial  to  the  earth,  for  they  remove  waste  foods 
and  dead  plant  and  animal  matter.  But  if  we  wish  to 
guard  food  that  we  want  to  eat,  we  must  either  seal  it 
away  from  the  air,  or  we  must  treat  it  in  such  a  way 
that  destructive  plants  cannot  grow  in  it. 

205.   How  Does  Drying  Preserve  Food?  —  Drying  is 
one  way  of  treating  food  so  that  it  will  be  impossible 

222 


THE   PRESERVING  OF  FOODS 


223 


for  bacteria  to  attack  it.  Bacteria  and  other  germs  need 
moisture  for  growth,  just  as  a  human  being  does.  Al- 
though a  dried  apple  may  be  covered  with  spores,  they 
will  not  start  growing  until  there  is  enough  moisture 
present.  The  method  of  keeping  fruits  and  vegetables 
by  drying  them  was  practiced  by  our  'ancestors  long  ago. 
It  is  easy  and  requires  very  little  equipment.  Old  attics 
used  to  be  hung  with  dried  corn  and  apples ;  many  of 
the  medicines  were  dried  herbs.  In  the  dry  sections  of 
the  West  "  jerked 
beef  '  was  made  by 
cutting  the  meat  into 
strips  and  hanging  it 
out  of  doors  to  dry 
in  windy  weather. 

206.  How  Is  Meat 
Smoked  ?  Every 
prosperous  farmer,  up 
to  a  generation  ago, 
had  a  smoke  house. 

Before  the  days  of  refrigerator  cars  and  easy  access  to 
meat  markets,  the  farmer  killed  his  own  meat,  and  as 
the  meat  could  not  all  be  eaten  at  once,  some  of  it  had  to 
be  preserved,  or  protected  from  the  germs  of  the  air. 
It  was  hung  in  the  smoke  from  a  wood  fire  until  the  smoke 
had  not  only  given  a  delicious  flavor  to  the  meat,  but  also 
had  rendered  it  safe.  Smoke  is  a  preservative  because 
it  contains  a  substance  called  creosote. 

207.  What  are  Salting  and  Pickling  ?  -  -  Two  common 
home  preservatives  are  salt  and  vinegar;  they  season 


FIG.  121.  —  A  smoke  house  for  smoking  fish. 
The  smoke  passes  through  a  long  pipe  before  it 
enters  the  house,  in  order  that  it  may  be  cooled. 


224  JUNIOR  SCIENCE 

food  as  well  as  preserve  it.  Salt  and  vinegar  make 
solutions  in  which  the  germs  of  decay  cannot  live.  Salt- 
peter (which  the  chemist  calls  potassium  nitrate)  is  also 
used.  It  makes  the  red  color  of  meat  more  intense. 
You  know  how  red  "  corned  beef  "  is;  saltpeter  is  used 
in  preserving  it. 

208.  How  Does  Sugar  Preserve  Food?  —  Have  you 
ever  seen  your  mother  put  up  preserves,   or  jelly,   or 
candied   fruits?     She   does   not   seal   the   jars    or    cans 
tightly,  as  she  does  in  ordinary  canning.     Why  then  do 
not  the  germs  and  spores  of  the  air  fall  into  the  fruit 
and  cause  it  to  ferment  or  mold  ?     If  you  were  to  find  out 
how  much  sugar  is  used  in  "  preserving  "   fruits,   you 
would  have  the  answer :    the  amount  of  sugar  is  much 
larger  than  in  canning;  so  large  that  germs  cannot  live 
in  the  £ugar  solution. 

209.  What    are    the    Principles    of    Canning  ?-- The 
methods  of  preserving  food  by  smoking  and  by  the  use  of 
salt,  vinegar,  and  sugar  have  been  practiced  for  many 
centuries.     A  wonderful  step  in  progress  was  made  in 
the  nineteenth  century,  when  the  method  of  preserving 
food  by  sealing  it  tightly  in  glass  or  tin  cans  came  into 
general  use.     The  principles  of  canning  are  : 

(1)  to  sterilize  the  food,  that  is,  to  kill  any  bacteria  or  spores  which 
may  be  on  it ; 

(2)  to  seal  it  air-tight  and  prevent  the  entrance  of  any  more  bacteria 
or  spores. 

Fruits  and  vegetables  are  attacked  freely  by  germs 
from  the  air ;  in  canning,  the  food  is  cooked  until  the 


THE   PRESERVING  OF  FOODS 


225 


Escape  for  expanding 
md  steam 


temperature  becomes  too  high  for  the  germs  to  exist 
(212°  F.  or  higher). 

210.  What  are  the  Methods  of  Canning?  —  Several 
processes  are  used  in  canning.  The  oldest  is  the  "  open 
kettle  "  method.  The  food  is  put  into  a  kettle  and  boiled. 
Then  it  is  dipped  out,  put  into  a  thoroughly  cleaned  and 
sterilized  can,  and  sealed.  How 
is  the  can  sterilized,  or  freed  from 
germs  ? 

In  changing  the  food  from  kettle 
to  can,  there  is,  of  course,  some  little 
danger  that  bacteria  or  other  germs 
will  get  on  the  fruit.  There  is  also 
danger  that  germs  may  lurk  in  re- 
used can  covers,  if  they,  too,  are  not 
very  well  sterilized  by  thorough  boil- 
ing. The  cans  should  always  be  filled 
to  overflowing  and  no  air  bubbles 
should  be  left  in  them.  Why  ? 

The  newer  method  of  canning  is  the  "  cold- 
pack  ;'  method.  The  government  has  an  agricultural 
bulletin  devoted  to  the  description  of  this  process  ; 
it  gives  information  as  to  how  long  each  partic- 
ular food  should  be  cooked  and  how  each  should  be 
handled  (Fig.  122). 

If  fruit  is  to  be  canned,  it  is  made  ready,  placed  in  clean  cans, 
covered  with  a  sirup,  and  then  the  whole  can  is  heated  to,  the  tem- 
perature of  boiling  water  or  higher.  Sometimes  the  can  is  heated 
in  the  oven,  sometimes  by  steam ;  but  in  the  home  the  method  of 
immersing  the  can  is  most  often  used  (Fig.  123). 


FIG.  122.  —  The  steam 
canner,  with  a  ther- 
mometer. 


226  JUNIOR  SCIENCE 

Vegetables  are  first  "  blanched,"  that  is,  are  put  into  boiling  water 
for  a  short  time.  Then  they  are  chilled  by  cold  water  and  are  packed. 
Salt  and  sometimes  water  are  added  and  then  the  cans  are  heated. 
The  lids  are  put  on  the  cans  before  they  are  heated,  but  they  are  not 
sealed  tightly  until  the  can  is  taken  out  of  its  water  or  steam  bath. 
Vegetables  have  to  be  heated,  or  "  processed/'  as  we  call  it,  much 
longer  than  the  fruits.  The  reason  for  this  is  that  there  are  spores 
on  the  vegetables,  which  are  not  killed  by  heat  unless  the  heating  is 
carried  on  for  a  great  length  of  time. 

"  Intermittent  heating/'  that  is,  heating  several  times, 
is  often  used  to  preserve  vegetables ;  it  is  carried  out  by 

heating  the  can  of  vegetables  for 
a  little  while  on  each  of  three 
days.  The  first  heating  is  not 
long  enough  to  kill  all  the  spores, 
but  when  the  vegetable  begins  to 
cool  and  reaches  a  nice,  warm 

FIG.  123.  —  The  hot  water 

canner,  made  out  of  a  wash  temperature,  the  spores  that  re- 
om*  main  develop  into  the  growing 
stage.  The  next  day  the  can  is  heated,  and  as  the  bac- 
teria in  the  growing  stage  are  easily  destroyed,  the 
developed  spores  are  killed. 

The  cold-pack  method  makes  more  attractive  canned 
products  possible,  because  the  fruit  and  vegetables  are 
put  in  whole  and  are  not  handled  again;  hence  they 
keep  their  shape.  Tomatoes  canned  in  this  way  make 
salads  possible  in  the  winter.  The  flavor  and  color  are 
much  finer.  When  you  enter  a  house  in  which  canning 
is  being  done  by  the  open  kettle  method,  the  odor  of  the 
fruit  is  noticeable  even  though  the  cooking  is  being  done 
in  another  room.  Why?  Much  of  the  flavor  of  the 


THE   PRESERVING  OF   FOODS  227 

« 
fruit  is  lost  in  this  odor.     Much  of  the  color  is  lost,  too, 

by  the  open  heating.     When  fruit  is  cooked  in  the  can, 
its  flavor  and  color  are  retained. 

211.  Does  Canning  Pay?  —  Do  you  think  that  people 
ought  to  cultivate  the  habit  of  canning?     If  we  could 
once  see  the  amount  of  good  food  that  goes  to  waste  in 
the  ordinary  family  garden,  we  would  realize,  with  a 
shock,  that  there  is  no  better  way  to  practice  saving,  or 
thrift,  than  to  can  for  winter's  use  the  vegetables  and 
fruits  of  summer.     Think  of  it!     It  has  been  estimated 
that  half  of  all  the  fruit  and  vegetables  nature  grows  for 
us    are    wasted    every    year.     Sometimes    they    remain 
neglected  in   the  garden ;  sometimes  they  are  sent  to 
market  and  through  bad  methods  of  packing  or  selling 
are  allowed  to  spoil,  unsold. 

What  examples  of  avoidable  waste  of  food  do  you  know 
of  in  your  community?  How  could  such  waste  be 
remedied? 

212.  Canning    as    a   Factory   Industry.  —  Have    you 
ever  thought  how  canning  has  changed  qur  method  of 
living?     People  find  it  so  convenient  to  have  the  vege- 
tables of  summer  all  winter  long,  and  so  enjoy  having  on 
their  tables  the  perishable  products  of  distant  regions, 
that  the  canning  of  fruits,  vegetables,  fish,   and  meat 
has  become  one  of  the  large  industries  of  the  United 
States.     In  some  cases  the  food  is  partly  cooked  before 
it  is  canned.     This  is  true  of  sweet  corn.     Most  foods, 
however,   are  packed  cold.     After  the  cans  are  filled, 
they  are  capped  by  machinery  and  then  heated  —  usu- 
ally under  steam  pressure. 


228  JUNIOR  SCIENCE 

The  machinery  which  has  been  invented  for  the  filling  of  cans,  for 
moving  them,  and  for  heating  and  preparing  the  food  to  put  into  the 
cans,  makes  the  canning  process  very  easy  and  very  rapid.  Peas, 
for  example,  are  canned  in  great  quantities.  The  way  in  which  they 
are  graded  for  size  is  very  interesting.  The  peas  are  passed  over  sieves 
or  into  a  revolving  cylinder  having  four  sections,  each  with  different- 
sized  holes.  The  holes  in  the  first  cylinder  are  very  small,  those  of 
the  second  are  a  little  larger,  and  so  on.  The  smallest  peas  are  thus 
separated  out  first.  They  are  the  most  expensive. 

213.  Do  Preservatives  Harm  Foods?  —  Why  go  to  all 
this  trouble  to  preserve  food  by  heating  it  and  keeping  it 
in  air-tight  cans?     Why  not  put  into  the  food  a  small 
amount  of  some  chemical,  such  as  borax  or  formaldehyde, 
which  will  destroy  the  germs  and  prevent  natural  decay  ? 
The  answer  of  science  is  that  such  chemicals  or  preserva- 
tives are  either  poisons,  or  they  keep  our  food  from  di- 
gesting properly.     Food  so  preserved  does  us  little  good, 
but  is  largely  wasted.     In  addition  to  this,  food  of  poor 
quality,  or  slightly  rotted,  may  be  treated  with  preserva- 
tives and  then  sold  to  us  as  good  food. 

Children  are  in  great  danger  when  preservatives  are 
used  in  milk,  because  milk  forms  so  large  a  part  of  a 
child's  diet. 

Do  you  think  a  wise  housekeeper  will  consent  to  feed 
her  family  with  food  containing  injurious  chemicals,  or 
to  put  "  acids  "  in  her  canned  goods  just  to  save  herself 
the  trouble  of  canning  or  preserving  food  properly  ? 

214.  Exercises. —  1.   Give  the  reason  why  some  foods  must   be 
canned  if  you  wish  to  preserve  them. 

2.  Give  three  good  reasons  for  using  the  cold-pack  method  of 
canning. 


THE   PRESERVING  OF  FOODS  229 

3.  Why  must  you  not  seal  the  can  lid  tightly,  in  the   cold-pack 
method,  before  you  begin  heating? 

4.  If  a  tin  can  of  tomatoes  bulges  inward,  are  the  tomatoes  likely 
to  be  spoiled?     If  it  bulges  outwards?     Tell  why. 

5.  Why  is  a  "  tin  "  can,  that  is,  a  can  of  iron  covered  with  tin, 
used  instead  of  one  of  iron  alone?     Would  one  covered  with  copper  do 
as  well? 

6.  What  do  you  think  of  the  use  of  chemicals  to  preserve  the  color 
of  food,  that  is,  to  keep  peas  green  and  to  redden  canned   cherries? 
What  do  you  think  of  the  use  of  artificial  dyes  in  candies  ? 

7.  How  does  the  atmosphere's  pressure  help  to  keep  a  glass  fruit 
jar  tightly  sealed? 


APPENDIX 


TABLE  I.    THE  METRIC  SYSTEM 

1.  Length.    The  unit  of  length  is  the  meter  (39.37  in.). 

10  millimeters  (mm.)  =  l  centimeter  (cm.). 
10  centimeters  =1  decimeter  (dm.). 

10  decimeters  =1  meter  (m.). 

1,000  meters  =1  kilometer  (km.). 

Note  that  the  prefix  "  milli-  "  means  0.001,  as  mill  =  0.001  dollar; 
"  centi-  "  means  0.01,  as  cen£  =  0.01  dollar;  "  deci-  "  means  0.1  as 
dime  =  0.1  dollar.  "  Kilo-  "  means  1,000. 

2.  Square  Measure,  or  Area. 

100  square  millimeters  (sq.  mm.)  =  1  sq.  centimeter  (sq.  cm.) 
100  square  centimeters  =1  sq.  decimeter  (sq.  dm.). 

100  square  decimeters  =1  sq.  meter  (sq.  m.). 

3.  Cubic  Measure,  or  Volume.    The  unit  of  volume  is  the  liter,  which 

is  1  cu.  dm.,  or  1,000  c.c. 

1,000  cubic  millimeters  (cu.  mm.)  =  l  cubic  centimeter  (c.c). 

1,000  cubic  centimeters  =1  cubic  decimeter  (cu.  dm.). 

1  cubic  decimeter  =1  liter  (1.) 

10  liters  =  1  dekaliter  (dl.). 

10  dekaliters  =1  hectoliter  (hi.). 

10  hectoliters  =  1  kiloliter  (kl.). 

4.  Weight.     The  gram  is  the  weight  of  1  c.c.  water  at  4°  C. ;  1  liter  of 

water  at  4°  C.  weighs  1  kilogram. 
10  milligrams  (mg.)  =  l  centigram  (eg.). 
10  centigrams  =1  decigram  (dg.). 

10  decigrams  =  1  gram  (g.). 

1,000  grams  =1  kilogram  (kg.). 

1,000  kilograms  =  1  metric  ton. 

231 


232  APPENDIX 

TABLE  II.    EQUIVALENTS 

1.  Length. 

1  centimeter  =  0.3937  in. 

1  meter         =39.37  in.  =3.28  ft. 

1  kilometer  =1,000  m.  =  0.6214  mile. 

1  inch  =2.54  cm. 

1  foot  =  0.3048m. 

1  mile  =1.6094  km. 

2.  Area. 

1  sq.  cm.          =0.155  sq.  in. 

1  sq.  m.  =  10.764  sq.  ft.  =1.196  sq.  yd. 

100  in.  square  =  10,000  sq.  m.  =  1  hectare  =  2.47  acres. 

1  sq.  km.         =0.385  sq.  mile. 

3.  Volume. 

1  cu.  cm.  =  0.061  cu.  in. 

1  cu.  m.  =35.315  cu.  ft. 

1  liter      =  1,000  cu.  cm.  =1.0567  qt.  (U.  S.). 

4.  Weight. 

1  gram  =  15.4324  grains. 

1  kilogram  =  1,000  grams  =  2.2046  Ib. 

1  metric  ton  =  1,000  kg.  =  2,204.6  Ib. 

1  short,  or  net  ton  =2,000  Ib. 

1  long,  or  gross  ton  =2,240  Ib. 

1  grain  =0.0648  gram. 

1  ounce  (avoirdupois)  =28.35  grams. 

1  ounce  (troy)  =31.1  grams. 


APPENDIX  233 

TABLE  III.     DENSITIES   OF   SOME    SUBSTANCES 


Acetic  acid  *    ... 
Alcohol  (ethyl)*  .     . 

1.053 
0.794 

Magnesium       .     .     . 
Marble    

1.75 
2.7 

Aluminum  .... 
Brass 

2.67 
8.3 

Mercury  (at  0°  C.)    . 
Nickel     

13.596 

8.57 

Carbolic  acid   .     .     . 
Carbon  (charcoal)     . 
Carbon  (gas)    .     .     . 
Carbon  disulphide  * 
Chloroform  *   ... 
Clay  

0.95 
1.6 
1.8 
1.27 
1.5 
1.9 

Nitric  acid  (cone.)*  . 
Oil  (cottonseed) 
Oil  (linseed)      .     . 
Oil  (olive)    .... 
Oil  (turpentine)     . 
Phosphorus  (yellow) 

1.42 
0.926 
0.942 
0.918 
0.873 
1.83 

Coal  (anthracite) 
Coal  (soft)  .... 
Copper 

1.26  to  1.8 
1.2  to  1.5 
89 

Platinum      .... 
Potassium    .... 
Sand  (dry) 

21.5 
0.865 
1  4 

Cork 

0  24 

Silver 

10  57 

Diamond     .... 

3.53 

Sodium    

0.97 

Ether  *  

072 

Sulphur 

2.03 

Gasoline      .... 
Glass       

0.67 
2.6  to  3.6 

Sulphuric  acid  (cone.) 
Tin     

1.854 
7.29 

Glycerine     .     .     .  "    . 
Gold  

1.27 
19.3 

Water  at  0°  C.      .     . 
Water  at  4°  C       .     . 

0.999 
1.000 

Hydrochloric  acid 
(cone.)*  .... 
Ice      

1.22 
0.918 

Water  at  100°  C. 

Water  (sea)            .     . 
Wood  (hickory   dry) 

0.958 
1.026 
1  00 

Iodine     

4.95 

Wood  (maple   dry) 

064 

Iron   

7.8 

Wood  (white  oak  dry) 

086 

Kerosene     .... 
Lead  

0.79 
11.35 

Wood     (white     pine, 
dry) 

042 

Limestone  .... 

3.2 

Zinc    

6.9  to  7.2 

*Atl5°C. 


234 


APPENDIX 


TABLE  IV.    PERCENTAGE  COMPOSITION   OF  FOOD 
MATERIALS 


FOOD 

WATER 

PROTEID 

FAT 

CARBO- 
HYDRATES 

MIN- 
ERALS 

VALUE  OF 
1  LB.  IN 
LARGE 
CALORIES 

Aoples  . 

83.2 

0.2 

0.4 

15.9 

0.3 

315 

Beans  (dry)    .     .     . 
Beef  (round)  .     .     . 
Beef  (sirloin)        .     . 
Bread    

12.6 
68.2 
60.0 
35.3 

'  23.1 
20.5 
18.5 
9.2 

2.0 
10.1 
20.5 
1.3 

59.2 
53  1 

3.1 
1.2 
1.0 
1  1 

1,615 
805 
1,200 
1  215 

Butter  

10.5 

1.0 

85.0 

05 

30 

3  410 

Candy   

3.0 

96.5 

05 

1  785 

Cheese 

302 

283 

35  5 

1  8 

42 

2  070 

Chicken      .... 
Cornmeal  .... 

EffffS 

72.2 
15.0 

73.8 

24.4 
9.2 
14.9 

2.0 
3.8 
10.5 

70.6 

1.4 
1.4 

08 

540 
1,645 
721 

Fish  (salmon)      .     . 
Milk      .          ... 

63.6 
870 

21.6 
36 

13.4 
40 

47 

1.4 

0  7 

965 
325 

Mutton  (leg)  .     .     . 
Oatmeal     .... 
Oysters  .     .     .     .     . 
Peanuts      .... 
Pork  (fresh)    .     .     . 
Potatoes  (white) 
Potatoes  (sweet) 
Rice       

61.8 
7.6 
87.1 
9.2 
52.0 
78.3 
69.0 
12  0 

18.3 
15.1 

6.0 

25.8 
16.9 
2.2 
1.3 
80 

19.0 
7.1 
1.2 
38.6 
30.1 
0.1 
0.6 
20 

68.2 
3.7 
24.4 

18.4 
28.3 

77  0 

0.9 
2.0 
2.0 
2.0 
1.0 
1.0 
0.8 
1  0 

1,140 
1,850 
230 
2,560 
1,600 
385 
480 
1  700 

Strawberries   .     .     . 
Sugar     

90.4 

1.0 

0.6 

7.4 
100.0 

0.6 

180 
1,850 

Tomatoes  .... 
Walnuts  (English)   . 

95.3 

2.8 

0.8 
16.7 

0.4 
64.4 

3.2 

14.8 

0.3 
1.3 

80 
3,305 

GLOSSARY 


abdomen 

(ab-do'men) 

calorimeter 

(kal'o-rim'e-teT) 

acetic 

(a-set'ic) 

calyx 

(ka'lix) 

acetylene 

(a-set'i-len) 

canine 

(ka-nm') 

adenoids 

(ad'e-noid) 

canon 

(k£n'yon) 

aeronaut 

(a/er-6-naut) 

capillary 

(kap'il-a'ri) 

aeroplane 

(a'er-o-plan) 

carat 

(kar'at) 

albumin 

(al-bu'min) 

carbohydrate 

(kar'bo-hy'drat) 

alga 

(al'ga) 

carnivorous 

(kar-niv'6-rus) 

alluvial 

(al-lu'vi-al) 

cartilage 

(kar'ti-laj) 

ambergris 

(am'ber-gres) 

casein 

(ka'se-In) 

ameba 

(a-me'ba) 

Cassiopeia 

(kas'I-6-pe'ya) 

andirons 

(and'l'ern) 

cellulose 

(sel'u-los) 

anemia 

(a-ne'mi-a) 

Celsius 

(sel'si-us) 

aniline 

(an'i-lm) 

centigrade 

(sen'ti-grad) 

antitoxin 

(Sn'ti-tox'in) 

centimeter 

(sen'ti-me'ter) 

aorta 

(a-6r'ta) 

centrifugal 

(sen-trif'u-gal) 

aqueduct 

(ak'we-dukt) 

cerebellum 

(ser'e-bel'um) 

aqueous 

(ak'we-us) 

cerebrum 

(ser'e-briim) 

asbestos 

(as-bes'tos) 

chloride 

(klo'rid) 

avoirdupois 

(av'er-du-poiz') 

chlorine 

(klo'rin) 

chlorophyll 

(klo'ro-fil) 

bacilli 

(ba-sil'I) 

chyle 

(kll) 

bacteria 

(bak-te'ri-a) 

chyme 

(klm) 

barometer 

(ba-rom'e-tSr) 

cilia 

(sil'i-a) 

biceps 

(bi'seps) 

circuit 

(sur'kit) 

bituminous 

(bi-tum'i-niis) 

cirrus 

(sir'us) 

bronchial 

(bron'ki-al) 

citric 

(sit'rik) 

buoyant 

(boi'ant) 

coagulate 

(ko-ag'u-lat) 

cochineal 

(koch'I-nel) 

cactus 

(kak'tus) 

cocoon 

(ko-koon') 

caisson 

(ka/son) 

cohesion 

(ko-he'shun) 

calcium 

(kai'si-um) 

composite 

(k5m-p6z'it) 

calorie 

(kaF6-ri) 

conifer 

(ko'ni-fer) 

235 


236 


GLOSSARY 


constellation 

(kon'stel-a'shun) 

galaxy 

(gal'aks-i) 

contagious 

(k6n-ta'jfis) 

galena 

(ga-le'na) 

convection 

(kon-vek'shun) 

Galileo 

(gal'i-le'6) 

corolla 

(ko-rol'a) 

Galvani 

(gal-va/ne) 

corpuscle 

(kdr'pus'l) 

galvanize 

(gal'van-iz) 

cotyledon 

(kot'I-le'dun) 

gelatine 

(jel'a-tm) 

creosote 

(kre'6-sot) 

germicide 

(jerm'i-sld) 

crescent 

(kres'ent) 

glacier 

(gla/sher) 

croquette 

(kro-kef) 

glycerine 

(glis'er-in) 

Crustacea 

(krus-ta'she-a; 

crystalline 

(kris'tal-m) 

hematite 

(hem'a-tit) 

cumulus 

(ku'mu-lus) 

hemoglobin 

(he'mo-glo'bm) 

cyclone 

(si'klon) 

hemorrhage 

(hem'o-raj) 

hepatica 

(he-pat'i-ka) 

deciduous 

(de-sid'u-us) 

hibernate 

(hi'ber-nat) 

decimeter 

(dgs'i-me'ter) 

horizon 

(ho-rl'zon) 

diameter 

(di-am'e-ter) 

hydrochloric 

(hi'dro-klor'ik) 

diaphragm 

(di'a-fram) 

hydrogen 

(hl;dro-gen) 

dietetics 

(di-S-tet'iks) 

hydroxide 

(hl-drox'-id) 

dioxide 

(di-6x'id) 

hygiene 

(hi'ji-en) 

diphtheria 

(dif-the'ri-a) 

dirigible 

(dir'I-jib'l) 

igloo 

(ig'loo) 

dynamo 

(di'na-mo) 

immune 

(i-mun') 

incisor 

(m-si'ser) 

eclipse 

(e-klips') 

incubation 

(in'ku-ba'shiin) 

effervesce 

(ef-6r-ves') 

inertia 

(m-er'shi-a) 

electrolysis 

(e-lek-trol'I-sis) 

inoculation 

(m-6k'u-la'shun) 

embryo 

(em'bri-6) 

insulator 

(m'su-la'ter) 

emulsion 

(e-mul'shun) 

intestine 

(Tn-tes'tm) 

enamel 

(en-am'61) 

isobar 

(i'so-bar) 

environment 

(en-vir'un-ment) 

isolation 

(rso-la'shun) 

epidemic 

(6p'i-dem'ik) 

isotherm 

(i'so-therm) 

epidermis 

(6p'i-dgr'mis) 

esophagus 

(e-sof'a-gus) 

kilometer 

(kil'6-me'ter) 

experiment 

(eks-per'i-ment) 

lactic 

(lak'tik) 

filings 

(fil'ings) 

la  grippe 

(la  grip') 

formaldehyde 

(for-mal'de-hid) 

larvae 

(lar've) 

fossil 

(fos'il) 

leaven 

(leVen) 

GLOSSARY 


237 


legume 

(leg'um) 

petiole 

(pet'I-61) 

Leyden 

(li'den) 

petrify 

(pfit/rf-fl) 

lichen 

(H'ken) 

phenomena 

(fe-nom'e-na) 

lunar 

(lu'nar) 

phosphate 

(fos'lat) 

phosphorescence 

(fos'for-es'ens) 

magnesium 

(mag-nes'i-iim) 

phosphorus 

(fos'for-iis) 

manganese 

(mfm'gaii-es) 

Pisa 

(pe'za) 

mercerize 

(mer'cer-Iz) 

plumule 

(ploo'mul) 

meteor 

(me'te-or) 

pneumatic 

(nu-mat'ik) 

microbe 

(mi'krob) 

Polaris 

(po-la'rls) 

millimeter 

(mil'i-me'ter) 

polyp 

(pol'ip) 

monsoon 

(mon-soon') 

posterior 

(pos-te'ri-er) 

mucous 

(mu'ktis) 

potassium 

(p5-tas'i-um) 

muriatic 

(inur'i-at'ik) 

proteid 

(pro'te-id) 

protoplasm 

(pro'to-plazm) 

neutralize 

(nu'tral-iz) 

pulmonary 

(pul'm5-na-n) 

nimbus 

(nim'bus) 

pyrometer 

(pl-rom'e-tgr) 

nitrogen 

(m'tro-jen) 

python 

(python) 

nitrogenous 

(nl-troj'6-nus) 

nucleus 

(nu'kle-us) 

quarantine 

(kw6r;an-ten) 

octopus 

(ok'to-piis) 

radiation 

(ra'di-a'shun) 

omnivorous 

(om-nivro-riis) 

refrigerator  . 

(re-frij'er-a-ter) 

opaque 

(o-pak') 

reservoir 

(res'gr-vwdr) 

organism 

(6r'gS,n-ism) 

respiration 

(res'  pi-ra  'shun) 

Orion 

(6-ri'on) 

retort 

(re-torf) 

oxide 

(ox'id) 

rotate 

(ro'tat) 

oxidize 

(ox'Id-Iz) 

salicylic 

(sal'i-sil'ik) 

palate 

(pal'at) 

saliva 

(sal-i'va) 

pancreatic 

(pan'kre-at'ik) 

saprophyte 

(sap'ro-fit) 

paraffin 

(par'a-fm) 

saturate 

(sat'u-rat) 

Pasteur 

(pas-turO 

sauteing 

(so-ta'ing) 

pendulum 

(pen'du-lum) 

sebaceous 

(se-ba'shus) 

penumbra 

(pe-num'bra) 

secrete 

(se-kref) 

per  capita 

(per  kap'i-ta) 

sepal 

(se'pal) 

perennial 

(per-en'I-al) 

silica 

(siFI-ka) 

permanganate 

(per-man'gan-at) 

Sirius 

(si'ri-us) 

peroxide 

(per-ox'id) 

slaked 

(slakd) 

238 


GLOSSARY 


sodium 

(so'di-um) 

tornado 

(tor-na'do) 

solution 

(so-lu'shun) 

Torricelli 

(tor-ri-tchel'e) 

species 

(spe'shez) 

tractor 

(tr-ak'tor) 

spectrum 

(spek'trum) 

trichinae 

(tri-kln'e) 

spinach 

(spm'ij) 

tuberculosis 

(tu-bur'ku-los'is) 

spontaneous 

(spon-ta'ne-us) 

turpentine 

(tur'pen-tin) 

stamen 

(sta/men) 

stipule 

(stip'ul) 

Uranus 

(yu'ra-niis) 

stratified 

(strat'i-fld) 

vaccination 

(vak'si-na'shun) 

stratus 

(stra'tus) 

vacuum 

(vak'u-um) 

sulphuric 

(sul-fur'ik) 

vertebra 

(ver'te-bra) 

vitreous 

(vit're-iis) 

tangent 

(tangent) 

vitriol 

(vit'ri-51) 

tartaric 

(tar-tar'ik) 

Volta 

(vdl'ta) 

Taurus 

(taw'rus) 

temperature 

(tem'per-a-tur) 

zenith 

(ze'mth) 

thermometer 

(th6r-m6mre-tgr) 

zodiac 

(zo'di-ak) 

INDEX 


(Numbers  Denote  Pages) 


Acids,  191 

Test  for,  195 
Acids, 

citric,  192 

hydrochloric,  193 

lactic,  192 

nitric,  193 

sulphuric,  193 

tartaric,  192 
Adhesion,  124 
Air,  13,  32 

compression  of,  17 

cooling  of,  16,  17 

heating  of,  16,  17,  61 

in  motion,  170 

in  weathering,  169 

moisture  in,  57 
Air  brake,  19 
Air  pressure,  21,  24 
Alcohol,  192,  220 
Aldebaran,  100 
Alloy,  181 
Alluvial  soil,  172 
Aluminum  bronze,  182 
Ammonia,  liquid,  144 
Andirons,  62 
Anemia,  210 
Anthracite,  186 
Artesian  wells,  154 
Ashes,  29 
Atmosphere,  21,  77,  163 

composition  of,  78 

Backlog,  62 
Bacteria,  41,  222,  223 
Baking,  214,  217 
Baking  powder,  218 
Ballast,  117 


Barometer,  23 

Bases,  194 

Bed  rock,  163 

Bituminous  coal,  186 

Blast  furnace,  180 

Blood  pressure,  25 

Blotter,  125 

Boat,  submarine,  19 

Body  heat,  73 

Body  temperature,  53 

Boiling,  of  food,  216 

Boiling,  of  water,  143 

Boiling  point,  69 

Brass,  182 

Breathing,  49,  52,  58 

Brick,  186 

Brimstone,  136 

British  Thermal  Unit,  72 

Broiling,  217 

Bronze,  182 

Burning,  48 

experiments  with,  29 
explanation  of,  32 

Cabbage,  purple,  195 

Caisson,  19 

Calcium,  210 

Calcium  carbonate,  48 

Calcium  phosphate,  138 

Calorie,  72 

Canals,  174 

Candle,  30,  38 

Canning,  methods  of,  225 

principles  of,  224 
Canning  factory,  227 
Capillary  action,  125 
Carat,  183 
Carbohydrates,  207 

239 


240 


INDEX 


Carbon,  39,  42 

burning  of,  43 

Carbon  dioxide,  42,  44,  78,  192,  220 
Cassiopeia,  100 
Cast  iron,  181 
Celsius,  69 

Center  of  gravity,  118 
Centigrade,  69 
Centrifugal  force,  122 
Charcoal,  42 
Charring,  42 
Chemical  change,  128 
Chlorine,  136 
Cirrus,  81 
Clay,  72 
Cleaning,  198 
Climate,  77,  147 
Clothing  materials,  198 
Clouds,  79,  81 
Coal,  184 
Cohesion,  124 
Coke,  43 
Collecting  air,  14 
Columbus,  4 
Combustion,  33 

spontaneous,  40 
Comets,  109 
Compound,  130 
Compressed  air,  18 
Compression  pump,  18 
Concrete,  187 
Conduction  of  heat,  63 
Constellation,  98,  99 
Convection,  64 
Cooking,  214 
Copper,  182 

alloys,  182 

sulphide,  137 
Core  of  earth,  163 
Cotton,  199 
Crane,  62 
Creosote,  223 
Crops,  174,  176 
Crust  of  earth,  163 
Cultivating,  173 
Cyclone,  86 

Dairying,  175 
Damper,  62 


Day,  95 

Decay,  40,  41,  49 
Degree  of  heat,  71 
Density,  115 
Dew,  78 
Dew  point,  78 
Diamond,  184 
Digestion,  214 
Dipper,  98 

Distances,  of  stars,  100 
Distillation,  159 
Diving  bell,  19 
Drops  of  liquid,  124 
Dry  cleaning,  204 
Drying  food,  222 
Dust,  78 

Earth,  95,  105 
Earth  shine,  109 
Eclipse,  4 
Egg,  117 
Electricity,  4 
Electrolysis,  129 
Element,  130 
Emulsion,  202 
Energy,  112,  121,  206 
Erosion,  167 
Evaporation,  144 
Experiment,  6 

Fahrenheit,  68 
Fats,  208 
Faucets,  155 
Fermentation,  191 
Fertility  of  soil,  175 
Fertilizers,  176 
Filter,  159 
Fire,  26 

burning  of,  28 

starting  of,  27 
Fire  engine,  47 
Fireless  cooker,  76 
Fireplaces,  61 
Fixed  stars,  99 
Flame,  28,  33 
Flavor,  214 
Flax,  199 
Flint  and  steel,  27 
Fog,  80 


INDEX 


241 


Food,  206,  214 
preserving  of,  222 

Force,  112,  120 

in  water  surface,  123 

Force  pump,  157 

Fore  stick,  62 

Fossils,  165 

Franklin,  4,  5 

Freezing  point,  69 

Friction,  121 

Frost,  78 

Frying,  217 

Fuel,  134 

Furnaces,  64,  65,  66 

Gale,  85 
Galileo,  22,  68 
Gasoline,  204 
German  silver,  182 
Glaciers,  171 
Gluten,  209 
Glycerine,  204 
Gold,  182 
Grand  Canon,  149 
Granite,  167,  186 
Grape  juice,  192 
Grate,  62 
Gravel,  172 
Gravitation,  113 
Gravity,  113 
Great  Bear,  99 
Gross  weight,  15 
Ground  glass,  20 
Growth,  206 

Hail,  81 

Hammer,  pneumatic,  19 
Hard  water,  160 
Heat,  28,  71 
Heating,  61 
Heat  capacity   147 
Heavenly  bodies,  95 
Hematite,  179 
Hemorrhage,  25 
Horizon,  97 
Hurricane,  85,  87 
.  Hydrochloric  acid,  45 
Hydrogen,  129 
burning  of,  133 


Hydrogen  —  Continued 

in  fuels,  134 

preparation  of,  130 

properties  of,  132 
Hydrogen  peroxide,  37 

Ice,  144,  170 
Ice  cream,  145 
Ice  sheets,  171 
Inertia,  119,  122 
Iron,  39,  179,  210 

cast,  181 

oxide,  39,  41 

wrought,  181 
Irrigation,  173 
Isobars,  90 
Isotherms,  90 

Jupiter,  105 

Kindling  temperature,  28,  34 

Land  breeze,  85 
Lava,  167 
Lead,  39,  181 
Leavening,  218 
Lichens,  195 
Lift  pump,  156 
Light,  28 
Lightning,  4 
Lime,  194 
Limestone,  48,  186 
Limewater,  194 
Linseed  oil,  40 
Litmus,  195 
Lye,  203 

Manganese  dioxide,  36,  37 
Mantle  rock,  163 
Marble,  44,  186 
Mars,  105 
Matches,  138 
Melting  ice,  72 
Mercury,  18,  23,  105 
Metals,  178 
Meteors,  109 
Milk,  192 
Milky  Way,  100 
Minerals,  178 
in  foods,  210 


242 


INDEX 


Mixtures,  130 
Monsoons,  85 
Moon,  4,  107 
Mortar,  187 
Muscle  fiber,  215 

Neptune,  105 
Net  weight,  15 
Neutralize,  196 
Newton,  112 
Niagara  Falls,  164 
Nimbus,  81 
Nitrogen,  32 
Nonconductor,  74 
North  star,  99 

Ores,  178 

Organic  substances,  178 

Orion,  100 

Outcrop,  164 

Oxidation,  39 

Oxygen,  32,  36,  38,  129 

Paint,  hardening  of,  39 
Parasite,  216 
Peat,  186 
Pendulum,  119 
Perspiration,  74 
Phenomenon,  5 
Phosphorus,  31,  127 
Physical  change,  128 
Pickling,  223 
Planets,  104,  123 
Plants,  as  food,  212 
Pleiades,  100 
Plow,  173 
Plumbing,  154 
Plumb  line,  114 
Pneumatic  hammer,  19 
Poles,  of  battery,  129 
Popgun,  17 

Potassium  chlorate,  36 
Potassium  hydroxide,  194 
Preservatives,  228 
Preserving  food,  222 
Pressure,  21 
Properties,  127 
Pumice,  167 


Pump,  156 

compression,  18 
force,  157 
lift,  156 

Radiation,  63 
Rain,  81 
Rainfall,  82 
Rain  gauge,  82 
Repair,  206 
Reservoirs,  174 
Resistance,  121 
Respiration,  53 
Rocks,  163 

Rotation  of  crops,  176 
Rusting,  40 

Safety  match,  139 
Salt,  134,  196 
Salting,  223 
Saltpeter,  224 
Salts,  196 
Sand,  160,  172 
Sand  blast,  20 
Sandstone,  186 
Saturn,  105 
Scales,  laboratory,  15 
Science,  3,  4,  7 

at  home,  191 
Scientific,  6 
Sea  breeze,  85 
Sewerage,  152 
Shooting  stars,  110 
Silk,  199,  200 
Silt,  172 
Silver,  182 
Sky,  96 
Slag,  180 
Slaked  lime,  194 
Smelters,  179 
Smoke,  28 
Smoked  meat,  223 
Snow,  81 
Snowflakes,  82 
Soap,  202 
Soda  water,  46 
Sodium,  136 
Sodium  chloride,  136 

hydroxide,  194 


INDEX 


243 


Soil,  163 

alluvial,  172 

formation  of,  171 

structure  of,  172 
Solar  system,  105 
Solvent,  142 

Spontaneous  combustion,  40 
Springs,  154 
Star  map,  102,  103 
Starch,  209 
Steam,  143 
Steaming,  216 
Steel,  181 
Stones,  for  building,  186 

precious,  184 
Storms,  86 
Stoves,  62 
Stratify,  164 
Stratus,  81 
Submarine,  19 
Substances,  127 
Sugar,  192 

in  preserving  food,  224 
Sulphur,  30,  38,  136 
Sulphur  dioxide,  38,  137 
Sun,  104 
Sunrise,  98 
Sunset,  98 
Sunspots,  105 
Sweat,  75 

Tangent,  122 
Temperature,  67,  71 
Thermometer,  68 
Thunderstorms,  87 
Tilling  soil,  173 
Tinder,  27 
Tornado,  85,  87 
Torricelli,  22 
Tractor,  173 


Trap,  155 
Tuberculosis,  54 

Uranus,  105 

Vacuum,  23 
Ventilation,  53,  55 
Venus,  105 
Vinegar,  191,  223 

Washing,  198,  201 

Water,  78,  141,  163,  170,  211 

Water,  and  earth 's  surface,  148 

dangers  in,  157 

distillation  of,  159 

drinking,  158 

effect  on  climate,  147 

hard,  160 

purification  of,  160 

supply,  152 
Weather,  77 
Weathering,  167 
Weather  maps,  88,  89,  90 
Weight,  113 

of  air,  15,  16 
Wells,  153 

artesian,  154 
Westerlies,  85 
Wind,  172 
Winds,  84 
Wine,  192 
Wool,  74,  199,  200 
Wrought  iron,  181 

Yeast,  192,  219 

in  bread-making,  220 

Zenith,  97 
Zodiac,  104 


J05  49496' 


580473 


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